diff --git a/.config/webpack/development.js b/.config/webpack/development.js
index 029b8246ce..5602efd5a7 100644
--- a/.config/webpack/development.js
+++ b/.config/webpack/development.js
@@ -29,12 +29,30 @@ module.exports.create = function create() {
         commonjs: 'tiny-emitter',
         amd: 'tiny-emitter',
       },
+      exceljs: {
+        root: 'ExcelJS',
+        commonjs2: 'exceljs',
+        commonjs: 'exceljs',
+        amd: 'exceljs',
+      },
     };
     c.plugins.push(new WebpackBar({ name: ` ${PACKAGE_FILENAME}.js` }));
   });
 
   configFull.forEach(function(c) {
     c.output.filename = `${PACKAGE_FILENAME}.full.js`;
+    // The 'full' bundle inlines HyperFormula's own dependencies, but exceljs is
+    // kept external: it is large and its transitive licenses would break the
+    // single-preamble bundle invariant. xlsx import/export in the UMD 'full'
+    // build therefore requires providing exceljs (global `ExcelJS`) separately.
+    c.externals = {
+      exceljs: {
+        root: 'ExcelJS',
+        commonjs2: 'exceljs',
+        commonjs: 'exceljs',
+        amd: 'exceljs',
+      },
+    };
     c.plugins.push(new WebpackBar({ name: ` ${PACKAGE_FILENAME}.full.js` }));
   });
 
diff --git a/docs/guide/file-import.md b/docs/guide/file-import.md
index 1c9d04d278..ed677d2e50 100644
--- a/docs/guide/file-import.md
+++ b/docs/guide/file-import.md
@@ -1,69 +1,121 @@
-# File import
+# File import and export
 
-Import XLSX and CSV files into HyperFormula.
+Import and export XLSX files, and import CSV files, with HyperFormula.
 
 ## Overview
 
-HyperFormula has no built-in file import functionality. But its [factory methods](../api/classes/hyperformula.md#factories) use standard JavaScript data types, for easy integration with any way of importing data.
-
-## Import CSV files
-
-To import CSV files, use a third-party [CSV parser](https://www.npmjs.com/search?q=csv) (e.g., [PapaParse](https://www.npmjs.com/package/papaparse) or [csv-parse](https://www.npmjs.com/package/csv-parse)). Then pass the result to HyperFormula as a JavaScript array.
+HyperFormula can import and export `.xlsx` files out of the box, using the
+[ExcelJS](https://www.npmjs.com/package/exceljs) library under the hood. Import
+with the [`buildFromFile`](../api/classes/hyperformula.md#buildfromfile) factory
+method and export with the [`toFile`](../api/classes/hyperformula.md#tofile)
+method.
+
+For any other format (for example CSV), HyperFormula's
+[factory methods](../api/classes/hyperformula.md#factories) accept standard
+JavaScript arrays, so you can plug in any third-party parser.
+
+::: tip
+Only **cell values and formulas** are imported and exported. Cell styling,
+number formats, merged cells, charts, images, data validation, and other
+Excel-specific features are **not** preserved — HyperFormula stores only
+values and formulas. Formula import assumes the English (`en`) function dialect.
+On export, formulas that use newer or dynamic-array Excel functions are written
+without Excel's internal `_xlfn.` prefix, so they may not resolve when the
+exported file is opened in real Excel.
+:::
 
 ## Import XLSX files
 
-To import XLSX files, use a third-party [XLSX parser](https://www.npmjs.com/search?q=xlsx) (e.g., [ExcelJS](https://www.npmjs.com/package/exceljs) or [xlsx](https://www.npmjs.com/package/xlsx)). Then pass the result to HyperFormula as a JavaScript array.
-
-### Example: Import XLSX files in Node
-
-This example uses [ExcelJS](https://www.npmjs.com/package/exceljs) to import XLSX files into HyperFormula.
+Pass the file's bytes (an `ArrayBuffer` or `Uint8Array`) to the asynchronous
+[`buildFromFile`](../api/classes/hyperformula.md#buildfromfile) factory method.
+Reading the file itself is left to your environment, so the same API works in
+both Node.js and the browser.
 
-See full example on [GitHub](https://github.com/handsontable/hyperformula-demos/tree/3.1.x/read-excel-file).
+### In Node.js
 
 ```js
-const ExcelJS = require('exceljs');
+const fs = require('fs');
 const { HyperFormula } = require('hyperformula');
 
-async function run(filename) {
-  const xlsxWorkbook = await readXlsxWorkbookFromFile(filename);
-  const sheetsAsJavascriptArrays = convertXlsxWorkbookToJavascriptArrays(xlsxWorkbook)
-  const hf = HyperFormula.buildFromSheets(sheetsAsJavascriptArrays, { licenseKey: 'gpl-v3' });
+async function importXlsx(filePath) {
+  const data = fs.readFileSync(filePath); // a Buffer (a Uint8Array)
+  const hf = await HyperFormula.buildFromFile(data, { licenseKey: 'gpl-v3' });
 
   console.log('Formulas:', hf.getSheetSerialized(0));
   console.log('Values:  ', hf.getSheetValues(0));
-}
 
-async function readXlsxWorkbookFromFile(filename) {
-  const workbook = new ExcelJS.Workbook();
-  await workbook.xlsx.readFile(filename);
-  return workbook;
+  return hf;
 }
+```
+
+### In the browser
+
+```js
+import { HyperFormula } from 'hyperformula';
 
-function convertXlsxWorkbookToJavascriptArrays(workbook) {
-  const workbookData = {};
+// `file` is a File obtained from an <input type="file"> element.
+async function importXlsx(file) {
+  const data = await file.arrayBuffer(); // an ArrayBuffer
+  const hf = await HyperFormula.buildFromFile(data, { licenseKey: 'gpl-v3' });
 
-  workbook.eachSheet((worksheet) => {
-    const sheetDimensions = worksheet.dimensions
-    const sheetData = [];
+  return hf;
+}
+```
 
-    for (let rowNum = sheetDimensions.top; rowNum <= sheetDimensions.bottom; rowNum++) {
-      const rowData = [];
+If the bytes cannot be read as an `.xlsx` file, `buildFromFile` rejects with an
+[`UnsupportedFileError`](../api/classes/unsupportedfileerror.md).
 
-      for (let colNum = sheetDimensions.left; colNum <= sheetDimensions.right; colNum++) {
-        const cell = worksheet.getCell(rowNum, colNum)
+## Export XLSX files
 
-        const cellData = cell.formula ? `=${cell.formula}` : cell.value;
-        rowData.push(cellData);
-      }
+The asynchronous [`toFile`](../api/classes/hyperformula.md#tofile) method returns
+the workbook's bytes as a `Uint8Array`. Writing those bytes is left to your
+environment.
 
-      sheetData.push(rowData);
-    }
+### In Node.js
 
-    workbookData[worksheet.name] = sheetData;
-  })
+```js
+const fs = require('fs');
 
-  return workbookData;
+async function exportXlsx(hf, filePath) {
+  const bytes = await hf.toFile();
+  fs.writeFileSync(filePath, bytes);
 }
+```
+
+### In the browser
 
-run('sample_file.xlsx');
+```js
+async function downloadXlsx(hf, fileName) {
+  const bytes = await hf.toFile();
+  const blob = new Blob([bytes], {
+    type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+  });
+
+  const url = URL.createObjectURL(blob);
+  const link = document.createElement('a');
+  link.href = url;
+  link.download = fileName;
+  link.click();
+  URL.revokeObjectURL(url);
+}
 ```
+
+## Import CSV files
+
+HyperFormula has no built-in CSV parser. Use a third-party
+[CSV parser](https://www.npmjs.com/search?q=csv) (e.g.,
+[PapaParse](https://www.npmjs.com/package/papaparse) or
+[csv-parse](https://www.npmjs.com/package/csv-parse)), then pass the resulting
+array to [`buildFromArray`](../api/classes/hyperformula.md#buildfromarray).
+
+## Advanced: custom XLSX handling
+
+If you need control over how the workbook is read or written (for example, to
+read cached values instead of formulas, or to handle Excel features outside
+HyperFormula's value-and-formula model), parse the file yourself with a
+third-party [XLSX parser](https://www.npmjs.com/search?q=xlsx) such as
+[ExcelJS](https://www.npmjs.com/package/exceljs) or
+[xlsx](https://www.npmjs.com/package/xlsx), convert the result to JavaScript
+arrays, and pass them to
+[`buildFromSheets`](../api/classes/hyperformula.md#buildfromsheets). See a full
+example on [GitHub](https://github.com/handsontable/hyperformula-demos/tree/3.1.x/read-excel-file).
diff --git a/package-lock.json b/package-lock.json
index 32585c79d1..b44cdac87c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,6 +10,7 @@
       "license": "GPL-3.0-only",
       "dependencies": {
         "chevrotain": "^6.5.0",
+        "exceljs": "^4.4.0",
         "tiny-emitter": "^2.1.0"
       },
       "devDependencies": {
@@ -27,7 +28,6 @@
         "@babel/preset-typescript": "^7.26.0",
         "@babel/register": "^7.25.9",
         "@babel/runtime": "^7.26.0",
-        "@types/exceljs": "^0.5.3",
         "@types/jasmine": "^5.1.4",
         "@types/jest": "^26.0.24",
         "@types/jsdom": "^21.1.7",
@@ -49,7 +49,6 @@
         "eslint-plugin-license-header": "^0.6.1",
         "eslint-plugin-prettier": "^5.2.1",
         "esm": "^3.2.25",
-        "exceljs": "^4.4.0",
         "full-icu": "^1.5.0",
         "jasmine": "^5.4.0",
         "jest": "^26.6.3",
@@ -176,6 +175,7 @@
       "integrity": "sha512-CGOfOJqWjg2qW/Mb6zNsDm+u5vFQ8DxXfbM09z69p5Z6+mE1ikP2jUXw+j42Pf1XTYED2Rni5f95npYeuwMDQA==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@babel/code-frame": "^7.29.0",
         "@babel/generator": "^7.29.0",
@@ -2344,6 +2344,7 @@
         }
       ],
       "license": "MIT",
+      "peer": true,
       "engines": {
         "node": ">=18"
       },
@@ -2367,6 +2368,7 @@
         }
       ],
       "license": "MIT",
+      "peer": true,
       "engines": {
         "node": ">=18"
       }
@@ -2479,7 +2481,6 @@
       "version": "4.3.5",
       "resolved": "https://registry.npmjs.org/@fast-csv/format/-/format-4.3.5.tgz",
       "integrity": "sha512-8iRn6QF3I8Ak78lNAa+Gdl5MJJBM5vRHivFtMRUWINdevNo00K7OXxS2PshawLKTejVwieIlPmK5YlLu6w4u8A==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "@types/node": "^14.0.1",
@@ -2494,14 +2495,12 @@
       "version": "14.18.63",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-14.18.63.tgz",
       "integrity": "sha512-fAtCfv4jJg+ExtXhvCkCqUKZ+4ok/JQk01qDKhL5BDDoS3AxKXhV5/MAVUZyQnSEd2GT92fkgZl0pz0Q0AzcIQ==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/@fast-csv/parse": {
       "version": "4.3.6",
       "resolved": "https://registry.npmjs.org/@fast-csv/parse/-/parse-4.3.6.tgz",
       "integrity": "sha512-uRsLYksqpbDmWaSmzvJcuApSEe38+6NQZBUsuAyMZKqHxH0g1wcJgsKUvN3WC8tewaqFjBMMGrkHmC+T7k8LvA==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "@types/node": "^14.0.1",
@@ -2517,7 +2516,6 @@
       "version": "14.18.63",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-14.18.63.tgz",
       "integrity": "sha512-fAtCfv4jJg+ExtXhvCkCqUKZ+4ok/JQk01qDKhL5BDDoS3AxKXhV5/MAVUZyQnSEd2GT92fkgZl0pz0Q0AzcIQ==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/@gar/promisify": {
@@ -3883,16 +3881,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/@types/exceljs": {
-      "version": "0.5.3",
-      "resolved": "https://registry.npmjs.org/@types/exceljs/-/exceljs-0.5.3.tgz",
-      "integrity": "sha512-a0PLZEJGbA4kHHoSS8cQ20ynIv17vCBV1reqsrX5ksQQb077YYvhEKC82lEq6/+mMufhk68KJ5jwugL3DKG8sQ==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "@types/node": "*"
-      }
-    },
     "node_modules/@types/express": {
       "version": "5.0.6",
       "resolved": "https://registry.npmjs.org/@types/express/-/express-5.0.6.tgz",
@@ -4078,7 +4066,8 @@
       "resolved": "https://registry.npmjs.org/@types/node/-/node-17.0.45.tgz",
       "integrity": "sha512-w+tIMs3rq2afQdsPJlODhoUEKzFP1ayaoyl1CcnwtIlsVe7K7bA1NGm4s3PraqTLlXnbIN84zuBlxBWo1u9BLw==",
       "dev": true,
-      "license": "MIT"
+      "license": "MIT",
+      "peer": true
     },
     "node_modules/@types/normalize-package-data": {
       "version": "2.4.4",
@@ -4320,6 +4309,7 @@
       "integrity": "sha512-VlJEV0fOQ7BExOsHYAGrgbEiZoi8D+Bl2+f6V2RrXerRSylnp+ZBHmPvaIa8cz0Ajx7WO7Z5RqfgYg7ED1nRhA==",
       "dev": true,
       "license": "BSD-2-Clause",
+      "peer": true,
       "dependencies": {
         "@typescript-eslint/scope-manager": "5.62.0",
         "@typescript-eslint/types": "5.62.0",
@@ -6309,6 +6299,7 @@
       "integrity": "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "bin": {
         "acorn": "bin/acorn"
       },
@@ -6413,6 +6404,7 @@
       "integrity": "sha512-fgFx7Hfoq60ytK2c7DhnF8jIvzYgOMxfugjLOSMHjLIPgenqa7S7oaagATUq99mV6IYvN2tRmC0wnTYX6iPbMw==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "fast-deep-equal": "^3.1.1",
         "fast-json-stable-stringify": "^2.0.0",
@@ -6615,7 +6607,6 @@
       "version": "5.3.2",
       "resolved": "https://registry.npmjs.org/archiver/-/archiver-5.3.2.tgz",
       "integrity": "sha512-+25nxyyznAXF7Nef3y0EbBeqmGZgeN/BxHX29Rs39djAfaFalmQ89SE6CWyDCHzGL0yt/ycBtNOmGTW0FyGWNw==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "archiver-utils": "^2.1.0",
@@ -6634,7 +6625,6 @@
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/archiver-utils/-/archiver-utils-2.1.0.tgz",
       "integrity": "sha512-bEL/yUb/fNNiNTuUz979Z0Yg5L+LzLxGJz8x79lYmR54fmTIb6ob/hNQgkQnIUDWIFjZVQwl9Xs356I6BAMHfw==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "glob": "^7.1.4",
@@ -6656,14 +6646,12 @@
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/isarray/-/isarray-1.0.0.tgz",
       "integrity": "sha512-VLghIWNM6ELQzo7zwmcg0NmTVyWKYjvIeM83yjp0wRDTmUnrM678fQbcKBo6n2CJEF0szoG//ytg+TKla89ALQ==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/archiver-utils/node_modules/readable-stream": {
       "version": "2.3.8",
       "resolved": "https://registry.npmjs.org/readable-stream/-/readable-stream-2.3.8.tgz",
       "integrity": "sha512-8p0AUk4XODgIewSi0l8Epjs+EVnWiK7NoDIEGU0HhE7+ZyY8D1IMY7odu5lRrFXGg71L15KG8QrPmum45RTtdA==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "core-util-is": "~1.0.0",
@@ -6679,14 +6667,12 @@
       "version": "5.1.2",
       "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.1.2.tgz",
       "integrity": "sha512-Gd2UZBJDkXlY7GbJxfsE8/nvKkUEU1G38c1siN6QP6a9PT9MmHB8GnpscSmMJSoF8LOIrt8ud/wPtojys4G6+g==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/archiver-utils/node_modules/string_decoder": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.1.1.tgz",
       "integrity": "sha512-n/ShnvDi6FHbbVfviro+WojiFzv+s8MPMHBczVePfUpDJLwoLT0ht1l4YwBCbi8pJAveEEdnkHyPyTP/mzRfwg==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "safe-buffer": "~5.1.0"
@@ -6953,7 +6939,6 @@
       "version": "3.2.6",
       "resolved": "https://registry.npmjs.org/async/-/async-3.2.6.tgz",
       "integrity": "sha512-htCUDlxyyCLMgaM3xXg0C0LW2xqfuQ6p05pCEIsXuyQ+a1koYKTuBMzRNwmybfLgvJDMd0r1LTn4+E0Ti6C2AA==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/async-each": {
@@ -7503,7 +7488,6 @@
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-1.0.2.tgz",
       "integrity": "sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/base": {
@@ -7556,7 +7540,6 @@
       "version": "1.5.1",
       "resolved": "https://registry.npmjs.org/base64-js/-/base64-js-1.5.1.tgz",
       "integrity": "sha512-AKpaYlHn8t4SVbOHCy+b5+KKgvR4vrsD8vbvrbiQJps7fKDTkjkDry6ji0rUJjC0kzbNePLwzxq8iypo41qeWA==",
-      "dev": true,
       "funding": [
         {
           "type": "github",
@@ -7617,7 +7600,6 @@
       "version": "1.6.52",
       "resolved": "https://registry.npmjs.org/big-integer/-/big-integer-1.6.52.tgz",
       "integrity": "sha512-QxD8cf2eVqJOOz63z6JIN9BzvVs/dlySa5HGSBH5xtR8dPteIRQnBxxKqkNTiT6jbDTF6jAfrd4oMcND9RGbQg==",
-      "dev": true,
       "license": "Unlicense",
       "engines": {
         "node": ">=0.6"
@@ -7637,7 +7619,6 @@
       "version": "0.3.0",
       "resolved": "https://registry.npmjs.org/binary/-/binary-0.3.0.tgz",
       "integrity": "sha512-D4H1y5KYwpJgK8wk1Cue5LLPgmwHKYSChkbspQg5JtVuR5ulGckxfR62H3AE9UDkdMC8yyXlqYihuz3Aqg2XZg==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "buffers": "~0.1.1",
@@ -7675,7 +7656,6 @@
       "version": "4.1.0",
       "resolved": "https://registry.npmjs.org/bl/-/bl-4.1.0.tgz",
       "integrity": "sha512-1W07cM9gS6DcLperZfFSj+bWLtaPGSOHWhPiGzXmvVJbRLdG82sH/Kn8EtW1VqWVA54AKf2h5k5BbnIbwF3h6w==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "buffer": "^5.5.0",
@@ -7687,7 +7667,6 @@
       "version": "3.4.7",
       "resolved": "https://registry.npmjs.org/bluebird/-/bluebird-3.4.7.tgz",
       "integrity": "sha512-iD3898SR7sWVRHbiQv+sHUtHnMvC1o3nW5rAcqnq3uOn07DSAppZYUkIGslDz6gXC7HfunPe7YVBgoEJASPcHA==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/bn.js": {
@@ -7871,7 +7850,6 @@
       "version": "1.1.14",
       "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.14.tgz",
       "integrity": "sha512-MWPGfDxnyzKU7rNOW9SP/c50vi3xrmrua/+6hfPbCS2ABNWfx24vPidzvC7krjU/RTo235sV776ymlsMtGKj8g==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "balanced-match": "^1.0.0",
@@ -8058,6 +8036,7 @@
         }
       ],
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "baseline-browser-mapping": "^2.10.12",
         "caniuse-lite": "^1.0.30001782",
@@ -8099,7 +8078,6 @@
       "version": "5.7.1",
       "resolved": "https://registry.npmjs.org/buffer/-/buffer-5.7.1.tgz",
       "integrity": "sha512-EHcyIPBQ4BSGlvjB16k5KgAJ27CIsHY/2JBmCRReo48y9rQ3MaUzWX3KVlBa4U7MyX02HdVj0K7C3WaB3ju7FQ==",
-      "dev": true,
       "funding": [
         {
           "type": "github",
@@ -8124,7 +8102,6 @@
       "version": "0.2.13",
       "resolved": "https://registry.npmjs.org/buffer-crc32/-/buffer-crc32-0.2.13.tgz",
       "integrity": "sha512-VO9Ht/+p3SN7SKWqcrgEzjGbRSJYTx+Q1pTQC0wrWqHx0vpJraQ6GtHx8tvcg1rlK1byhU5gccxgOgj7B0TDkQ==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": "*"
@@ -8148,7 +8125,6 @@
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/buffer-indexof-polyfill/-/buffer-indexof-polyfill-1.0.2.tgz",
       "integrity": "sha512-I7wzHwA3t1/lwXQh+A5PbNvJxgfo5r3xulgpYDB5zckTu/Z9oUK9biouBKQUjEqzaz3HnAT6TYoovmE+GqSf7A==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=0.10"
@@ -8172,7 +8148,6 @@
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diff --git a/package.json b/package.json
index e2c8d29d17..ae01b753a2 100644
--- a/package.json
+++ b/package.json
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-    "exceljs": "^4.4.0",
     "full-icu": "^1.5.0",
     "jasmine": "^5.4.0",
     "jest": "^26.6.3",
diff --git a/src/HyperFormula.ts b/src/HyperFormula.ts
index 566957270a..811e484ab1 100644
--- a/src/HyperFormula.ts
+++ b/src/HyperFormula.ts
@@ -49,6 +49,9 @@ import {FunctionRegistry, FunctionTranslationsPackage} from './interpreter/Funct
 import {FormatInfo} from './interpreter/InterpreterValue'
 import {LazilyTransformingAstService} from './LazilyTransformingAstService'
 import {ColumnSearchStrategy} from './Lookup/SearchStrategy'
+import {sheetsToXlsx} from './io/xlsx/exporter'
+import {loadXlsxWorkbook} from './io/xlsx/loadWorkbook'
+import {workbookToSheets} from './io/xlsx/importer'
 import {NamedExpression, NamedExpressionOptions, NamedExpressions} from './NamedExpressions'
 import {normalizeAddedIndexes, normalizeRemovedIndexes} from './Operations'
 import {
@@ -323,6 +326,47 @@ export class HyperFormula implements TypedEmitter {
     return this.buildFromEngineState(BuildEngineFactory.buildFromSheets(sheets, configInput, namedExpressions))
   }
 
+  /**
+   * Builds the engine from the raw bytes of an .xlsx file. The file is parsed and its
+   * worksheets are converted into sheets, keyed by worksheet name, exactly as if they had
+   * been passed to [[buildFromSheets]].
+   * Can be configured with the optional second parameter that represents a [[ConfigParams]].
+   * If not specified the engine will be built with the default configuration.
+   *
+   * v1 scope: no import options, no named expressions, no cell-format detection (see HF-107).
+   *
+   * @param {ArrayBuffer | Uint8Array} data - the raw bytes of an .xlsx file
+   * @param {Partial<ConfigParams>} configInput - engine configuration
+   *
+   * @returns {Promise<HyperFormula>} a promise that resolves to the built engine
+   *
+   * @throws [[UnsupportedFileError]] when `data` cannot be read as a valid .xlsx workbook
+   * (e.g. it is empty or not a well-formed .xlsx file)
+   * @throws [[SheetSizeLimitExceededError]] when a worksheet size exceeds the limits
+   *
+   * @example
+   * ```js
+   * // Node.js: read the file from disk first
+   * const fs = require('fs/promises');
+   * const buffer = await fs.readFile('example.xlsx');
+   * const hfInstance = await HyperFormula.buildFromFile(buffer, { licenseKey: 'gpl-v3' });
+   * ```
+   *
+   * @example
+   * ```js
+   * // Browser: read bytes from a File (e.g. an <input type="file"> element)
+   * const arrayBuffer = await file.arrayBuffer();
+   * const hfInstance = await HyperFormula.buildFromFile(arrayBuffer, { licenseKey: 'gpl-v3' });
+   * ```
+   *
+   * @category Factories
+   */
+  public static async buildFromFile(data: ArrayBuffer | Uint8Array, configInput: Partial<ConfigParams> = {}): Promise<HyperFormula> {
+    const workbook = await loadXlsxWorkbook(data)
+    const sheets = workbookToSheets(workbook)
+    return HyperFormula.buildFromSheets(sheets, configInput)
+  }
+
   /**
    * Builds an empty engine instance.
    * Can be configured with the optional parameter that represents a [[ConfigParams]].
@@ -1014,6 +1058,32 @@ export class HyperFormula implements TypedEmitter {
     return this._serialization.getAllSheetsSerialized()
   }
 
+  /**
+   * Exports the current engine state to `.xlsx` file bytes.
+   *
+   * v1 scope: values and formulas only, no styles/number-formats/merged cells
+   * (see HF-107). Formulas are serialized exactly as {@link getAllSheetsSerialized}
+   * would return them.
+   *
+   * @throws [[EvaluationSuspendedError]] when the evaluation is suspended
+   *
+   * @returns {Promise<Uint8Array>} a promise that resolves to the raw bytes of an .xlsx file
+   *
+   * @example
+   * ```js
+   * const hfInstance = HyperFormula.buildFromArray([
+   *  ['1', '2', '=A1+10'],
+   * ]);
+   *
+   * const bytes = await hfInstance.toFile();
+   * ```
+   *
+   * @category Sheets
+   */
+  public async toFile(): Promise<Uint8Array> {
+    return sheetsToXlsx(this.getAllSheetsSerialized())
+  }
+
   /**
    * Updates the config with given new metadata. It is an expensive operation, as it might trigger rebuilding the engine and recalculation of all formulas.
    *
diff --git a/src/errors.ts b/src/errors.ts
index 66a73a2add..316987cc3c 100644
--- a/src/errors.ts
+++ b/src/errors.ts
@@ -392,3 +392,15 @@ export class AliasAlreadyExisting extends Error {
     super(`Alias id ${name} in plugin ${pluginName} already defined as a function or alias.`)
   }
 }
+
+/**
+ * Error thrown when a file cannot be read as a supported spreadsheet format,
+ * e.g. when its byte buffer is empty or cannot be parsed as an .xlsx workbook.
+ */
+export class UnsupportedFileError extends Error {
+  constructor(public readonly reason: 'empty' | 'unparseable', detail?: string) {
+    super(detail === undefined
+      ? `Unsupported or unreadable file (${reason})`
+      : `Unsupported or unreadable file (${reason}): ${detail}`)
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index 4039d4a209..4698a2b598 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -42,7 +42,8 @@ import {
   SheetSizeLimitExceededError,
   SourceLocationHasArrayError,
   TargetLocationHasArrayError,
-  UnableToParseError
+  UnableToParseError,
+  UnsupportedFileError
 } from './errors'
 import {ExportedCellChange, ExportedChange, ExportedNamedExpressionChange} from './Exporter'
 import {HyperFormula} from './HyperFormula'
@@ -102,6 +103,7 @@ class HyperFormulaNS extends HyperFormula {
   public static SourceLocationHasArrayError = SourceLocationHasArrayError
   public static TargetLocationHasArrayError = TargetLocationHasArrayError
   public static UnableToParseError = UnableToParseError
+  public static UnsupportedFileError = UnsupportedFileError
 }
 
 const defaultLanguage = Config.defaultConfig.language
@@ -183,5 +185,6 @@ export {
   SourceLocationHasArrayError,
   TargetLocationHasArrayError,
   UnableToParseError,
+  UnsupportedFileError,
   SerializedNamedExpression,
 }
diff --git a/src/io/xlsx/exporter.ts b/src/io/xlsx/exporter.ts
new file mode 100644
index 0000000000..8089738894
--- /dev/null
+++ b/src/io/xlsx/exporter.ts
@@ -0,0 +1,52 @@
+/**
+ * @license
+ * Copyright (c) 2025 Handsoncode. All rights reserved.
+ */
+
+import {RawCellContent} from '../../CellContentParser'
+
+/**
+ * Converts HF's serialized sheets (as returned by
+ * {@link HyperFormula#getAllSheetsSerialized}) into `.xlsx` file bytes.
+ *
+ * Pure and async (ExcelJS's writer is async); does not touch a live engine.
+ *
+ * v1 mapping (deliberately minimal, see HF-107 task brief):
+ * - a `null`/`undefined` cell is left unset, so it reloads blank (not `0`/`''`).
+ * - a formula string (`cell[0] === '='`) becomes an ExcelJS formula cell.
+ * - `number` | `string` | `boolean` | `Date` pass through as-is.
+ *
+ * Values and formulas only &mdash; no styles, number formats, or merged cells.
+ */
+export async function sheetsToXlsx(sheets: Record<string, RawCellContent[][]>): Promise<Uint8Array> {
+  const ExcelJS = await import(/* webpackMode: "eager" */ 'exceljs')
+  const workbook = new ExcelJS.Workbook()
+
+  for (const sheetName of Object.keys(sheets)) {
+    const worksheet = workbook.addWorksheet(sheetName)
+    const rows = sheets[sheetName]
+
+    for (let r = 0; r < rows.length; r++) {
+      const row = rows[r]
+
+      for (let c = 0; c < row.length; c++) {
+        const cell = row[c]
+
+        if (cell == null) {
+          continue
+        }
+
+        const xc = worksheet.getCell(r + 1, c + 1)
+
+        if (typeof cell === 'string' && cell[0] === '=') {
+          xc.value = {formula: cell.slice(1)}
+        } else {
+          xc.value = cell
+        }
+      }
+    }
+  }
+
+  const buffer = await workbook.xlsx.writeBuffer()
+  return Uint8Array.from(buffer as Buffer)
+}
diff --git a/src/io/xlsx/importer.ts b/src/io/xlsx/importer.ts
new file mode 100644
index 0000000000..d7ae54ff1f
--- /dev/null
+++ b/src/io/xlsx/importer.ts
@@ -0,0 +1,108 @@
+/**
+ * @license
+ * Copyright (c) 2025 Handsoncode. All rights reserved.
+ */
+
+import type {Cell, Workbook, Worksheet} from 'exceljs'
+import {RawCellContent} from '../../CellContentParser'
+import {Sheet, Sheets} from '../../Sheet'
+
+/**
+ * Converts an already-loaded ExcelJS {@link Workbook} into HyperFormula's
+ * {@link Sheets} shape.
+ *
+ * Pure and synchronous: byte-loading happens upstream in `loadXlsxWorkbook`.
+ *
+ * v1 mapping (deliberately minimal, see HF-107 task brief):
+ * - a formula cell (`cell.formula != null`) becomes the string `'=' + formula`.
+ * - `null`/`undefined` values become `null`.
+ * - a `Date` value passes through as-is (best-effort).
+ * - `number` | `string` | `boolean` pass through as-is.
+ * - any other (object-valued: error / rich text / hyperlink) cell falls back
+ *   to `cell.text` so we never emit the raw object.
+ *
+ * Excel's `_xlfn.` / `_xlws.` function-name prefixes are stripped from
+ * formula strings (see {@link stripFunctionPrefixes}); shared formulas and
+ * cross-sheet references already come back correctly rebased/verbatim from
+ * ExcelJS, so no further formula rewriting is needed.
+ *
+ * A full Excel/HF error-token table is out of scope here (deferred).
+ */
+export function workbookToSheets(workbook: Workbook): Sheets {
+  const sheets: Sheets = {}
+
+  workbook.eachSheet((worksheet: Worksheet) => {
+    sheets[worksheet.name] = worksheetToSheet(worksheet)
+  })
+
+  return sheets
+}
+
+/**
+ * Builds a rectangular {@link Sheet} from a worksheet's used range
+ * (1..rowCount x 1..columnCount), mapping ExcelJS's 1-based coordinates to
+ * the 0-based array.
+ */
+function worksheetToSheet(worksheet: Worksheet): Sheet {
+  const rowCount = worksheet.rowCount ?? 0
+  const columnCount = worksheet.columnCount ?? 0
+
+  if (rowCount === 0) {
+    return []
+  }
+
+  const sheet: Sheet = []
+
+  for (let r = 1; r <= rowCount; r++) {
+    const row = worksheet.getRow(r)
+    const rowContent: RawCellContent[] = []
+
+    for (let c = 1; c <= columnCount; c++) {
+      rowContent.push(cellToRawContent(row.getCell(c)))
+    }
+
+    sheet.push(rowContent)
+  }
+
+  return sheet
+}
+
+/**
+ * Strips Excel's internal `_xlfn.` / `_xlws.` function-name prefixes.
+ *
+ * Excel stores newer/relocated functions (e.g. `XLOOKUP`, dynamic-array
+ * functions) with a `_xlfn.` prefix, and some with a combined
+ * `_xlfn._xlws.` prefix, in the raw formula string. Left in place, HF would
+ * fail to recognize the function name (`_xlfn.XLOOKUP` → `#NAME?`) even when
+ * it natively supports the function.
+ *
+ * NOTE: this operates on the whole formula string, so a matching substring
+ * inside a string literal (e.g. `="_xlfn."`) would also be rewritten. That
+ * edge case is not handled here — accepted best-effort limitation for v1.
+ */
+function stripFunctionPrefixes(formula: string): string {
+  return formula.replace(/_xlfn\.|_xlws\./g, '')
+}
+
+/** Maps a single ExcelJS cell to a HyperFormula {@link RawCellContent} per the v1 mapping rule. */
+function cellToRawContent(cell: Cell): RawCellContent {
+  if (cell.formula != null) {
+    return '=' + stripFunctionPrefixes(cell.formula)
+  }
+
+  const value = cell.value
+
+  if (value == null) {
+    return null
+  }
+
+  if (value instanceof Date) {
+    return value
+  }
+
+  if (typeof value === 'number' || typeof value === 'string' || typeof value === 'boolean') {
+    return value
+  }
+
+  return cell.text ?? null
+}
diff --git a/src/io/xlsx/loadWorkbook.ts b/src/io/xlsx/loadWorkbook.ts
new file mode 100644
index 0000000000..c36dce2669
--- /dev/null
+++ b/src/io/xlsx/loadWorkbook.ts
@@ -0,0 +1,34 @@
+/**
+ * @license
+ * Copyright (c) 2025 Handsoncode. All rights reserved.
+ */
+
+import type {Workbook} from 'exceljs'
+import {UnsupportedFileError} from '../../errors'
+
+/**
+ * Loads raw xlsx bytes into an ExcelJS {@link Workbook}.
+ *
+ * v1 scope: attempt the ExcelJS load and wrap any failure. Byte-signature /
+ * ZIP-magic / CFB format detection is deliberately out of scope (YAGNI).
+ */
+export async function loadXlsxWorkbook(data: ArrayBuffer | Uint8Array): Promise<Workbook> {
+  if (data.byteLength === 0) {
+    throw new UnsupportedFileError('empty')
+  }
+
+  // Copy to a fresh, zero-offset Uint8Array (works in Node and the browser
+  // without pulling in the Node `Buffer` polyfill). `.slice()` on a subarray
+  // view copies exactly the view's logical bytes, so byteOffset is honored.
+  const bytes = data instanceof Uint8Array ? data.slice() : new Uint8Array(data)
+
+  try {
+    const ExcelJS = await import(/* webpackMode: "eager" */ 'exceljs')
+    const workbook = new ExcelJS.Workbook()
+    await workbook.xlsx.load(bytes.buffer)
+    return workbook
+  } catch (e) {
+    const detail = e instanceof Error ? e.message : String(e)
+    throw new UnsupportedFileError('unparseable', detail)
+  }
+}
diff --git a/tsconfig.json b/tsconfig.json
index 812d955676..d8ef6d31bd 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -8,8 +8,8 @@
     /* Basic Options */
     "target": "es6",
     /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
-    "module": "es2015",
-    /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
+    "module": "es2020",
+    /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. es2020 (was es2015) is required for the lazy `import('exceljs')` dynamic import; emit is unchanged for every module that does not use dynamic import / import.meta. */
     "lib": [
       "es6",
       "dom",