diff --git a/src/main/DocxFontEmbedder.js b/src/main/DocxFontEmbedder.js
new file mode 100644
index 0000000..9458c08
--- /dev/null
+++ b/src/main/DocxFontEmbedder.js
@@ -0,0 +1,119 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const JSZip = require('jszip');
+
+const REL_NS = 'http://schemas.openxmlformats.org/package/2006/relationships';
+
+function generatedRId(idx) {
+  return `rIdFont${idx}`;
+}
+
+async function patchZipWithFonts(inputPath, fonts) {
+  const buf = fs.readFileSync(inputPath);
+  const zip = await JSZip.loadAsync(buf);
+  const existingFontNames = new Set();
+
+  // Detect prior embeds (idempotency: skip TTF files already present).
+  for (const f of Object.keys(zip.files)) {
+    if (zip.files[f].name && /^word\/fonts\//.test(zip.files[f].name)) {
+      existingFontNames.add(path.basename(f));
+    }
+  }
+
+  for (let i = 0; i < fonts.length; i++) {
+    const { path: fontPath } = fonts[i];
+    const fname = path.basename(fontPath);
+    const wordPath = `word/fonts/${fname}`;
+    if (!existingFontNames.has(fname)) {
+      zip.file(wordPath, fs.readFileSync(fontPath));
+      existingFontNames.add(fname);
+    }
+  }
+
+  // Build/replace word/fontTable.xml so Word knows the family and where to
+  // fetch the embedded TTF data.
+  const fontTableXml =
+    `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>\n` +
+    `<w:fonts xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/main">\n` +
+    fonts
+      .map((f, i) =>
+        `  <w:font w:name="${f.family}"><w:embedRegular r:id="${generatedRId(i)}" xmlns:r="${REL_NS}"/></w:font>`
+      )
+      .join('\n') +
+    `\n</w:fonts>\n`;
+
+  zip.file('word/fontTable.xml', fontTableXml);
+
+  // Patch [Content_Types].xml — add Override for /word/fontTable.xml and each TTF.
+  const ctPath = '[Content_Types].xml';
+  let ct = await zip.file(ctPath).async('string');
+  if (!ct.includes('PartName="/word/fontTable.xml"')) {
+    ct = ct.replace(
+      '</Types>',
+      '<Override PartName="/word/fontTable.xml" ContentType="application/vnd.openxmlformats-officedocument.wordprocessingml.fontTable+xml"/></Types>'
+    );
+  }
+  for (const f of fonts) {
+    const ttfCt = 'application/x-font-ttf';
+    const filePart = `/word/fonts/${path.basename(f.path)}`;
+    if (!ct.includes(`PartName="${filePart}"`)) {
+      ct = ct.replace('</Types>', `<Override PartName="${filePart}" ContentType="${ttfCt}"/></Types>`);
+    }
+  }
+  if (!ct.includes('Default Extension="ttf"')) {
+    ct = ct.replace('</Types>', '<Default Extension="ttf" ContentType="application/x-font-ttf"/></Types>');
+  }
+  zip.file(ctPath, ct);
+
+  // Patch word/_rels/document.xml.rels — relationships for fontTable + each font.
+  const relsPath = 'word/_rels/document.xml.rels';
+  if (!zip.files[relsPath]) {
+    zip.file(
+      relsPath,
+      `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>\n<Relationships xmlns="${REL_NS}"/>`
+    );
+  }
+  let rels = await zip.file(relsPath).async('string');
+  if (!rels.includes('fontTable.xml')) {
+    rels = rels.replace(
+      '</Relationships>',
+      `<Relationship Id="${generatedRId(fonts.length)}" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/fontTable" Target="fontTable.xml"/></Relationships>`
+    );
+  }
+  for (let i = 0; i < fonts.length; i++) {
+    const fname = path.basename(fonts[i].path);
+    if (!rels.includes(fname)) {
+      rels = rels.replace(
+        '</Relationships>',
+        `<Relationship Id="${generatedRId(i)}" Type="http://schemas.microsoft.com/office/2011/relationships/font" Target="fonts/${fname}"/></Relationships>`
+      );
+    }
+  }
+  zip.file(relsPath, rels);
+
+  // Patch word/styles.xml — bind SourceCode/VerbatimChar styles to the family.
+  const stylesPath = 'word/styles.xml';
+  if (zip.files[stylesPath]) {
+    let styles = await zip.file(stylesPath).async('string');
+    const family = fonts[0].family;
+    if (!styles.includes(`w:ascii="${family}"`)) {
+      styles = styles.replace(
+        /(<w:style[^>]*w:styleId="(?:SourceCode|VerbatimChar)"[^>]*>)/,
+        `$1<w:rPr><w:rFonts w:ascii="${family}" w:hAnsi="${family}" w:cs="${family}"/></w:rPr>`
+      );
+    }
+    zip.file(stylesPath, styles);
+  }
+
+  const outBuf = await zip.generateAsync({ type: 'nodebuffer' });
+  fs.writeFileSync(inputPath, outBuf);
+  return inputPath;
+}
+
+async function embed(docxPath, fonts) {
+  return patchZipWithFonts(docxPath, fonts);
+}
+
+module.exports = { embed };
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diff --git a/tests/docx-font-embedder.test.js b/tests/docx-font-embedder.test.js
new file mode 100644
index 0000000..308511f
--- /dev/null
+++ b/tests/docx-font-embedder.test.js
@@ -0,0 +1,44 @@
+const fs = require('fs');
+const path = require('path');
+const JSZip = require('jszip');
+const DocxFontEmbedder = require('../src/main/DocxFontEmbedder');
+
+describe('DocxFontEmbedder.embed', () => {
+  const dir = path.join(__dirname, 'fixtures-docx');
+  const docxPath = path.join(dir, 'in.docx');
+  const fontPath = path.join(dir, 'fake.ttf');
+
+  beforeAll(async () => {
+    fs.mkdirSync(dir, { recursive: true });
+    fs.writeFileSync(fontPath, 'fake-ttf-data');
+    const zip = new JSZip();
+    zip.file('[Content_Types].xml', '<?xml version="1.0"?><Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"></Types>');
+    zip.file('_rels/.rels', '<?xml version="1.0"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"></Relationships>');
+    zip.file('word/document.xml', '<?xml version="1.0"?><w:document xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/main"><w:body/></w:document>');
+    zip.file('word/styles.xml', '<?xml version="1.0"?><w:styles xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/main"><w:style w:type="character" w:styleId="SourceCode"><w:name w:val="Source Code"/></w:style></w:styles>');
+    fs.writeFileSync(docxPath, await zip.generateAsync({ type: 'nodebuffer' }));
+  });
+
+  afterAll(() => fs.rmSync(dir, { recursive: true, force: true }));
+
+  test('embeds TTF and patches fontTable.xml + styles.xml', async () => {
+    const out = await DocxFontEmbedder.embed(docxPath, [
+      { path: fontPath, family: 'JetBrains Mono', weight: 400 },
+    ]);
+    const zip = await JSZip.loadAsync(fs.readFileSync(out));
+    expect(Object.keys(zip.files).some((f) => f.startsWith('word/fonts/'))).toBe(true);
+    const fontTable = zip.file('word/fontTable.xml') ? await zip.file('word/fontTable.xml').async('string') : '';
+    expect(fontTable).toContain('JetBrains Mono');
+    expect(fontTable).toMatch(/<w:embedRegular/);
+    const styles = await zip.file('word/styles.xml').async('string');
+    expect(styles).toMatch(/<w:rFonts[^>]*w:ascii="JetBrains Mono"/);
+  });
+
+  test('is idempotent: running twice does not double-embed', async () => {
+    const once = await DocxFontEmbedder.embed(docxPath, [{ path: fontPath, family: 'JetBrains Mono', weight: 400 }]);
+    const twice = await DocxFontEmbedder.embed(once, [{ path: fontPath, family: 'JetBrains Mono', weight: 400 }]);
+    const zip = await JSZip.loadAsync(fs.readFileSync(twice));
+    const fontEntries = Object.keys(zip.files).filter((f) => /^word\/fonts\/[^/]+\.ttf$/.test(f));
+    expect(fontEntries.length).toBe(1);
+  });
+});
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