diff --git a/src/main/DocxFontEmbedder.js b/src/main/DocxFontEmbedder.js
new file mode 100644
index 0000000..8ff701a
--- /dev/null
+++ b/src/main/DocxFontEmbedder.js
@@ -0,0 +1,46 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const JSZip = require('jszip');
+
+const FONT_TABLE_PATH = 'word/fontTable.xml';
+const FONT_TABLE_RELS_PATH = 'word/_rels/fontTable.xml.rels';
+
+function fontTableXml(family) {
+  return `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<w:fonts xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main">
+  <w:font w:name="${family}">
+    <w:panose1 w:val="020F0502020204030204"/>
+    <w:charset w:val="00"/>
+    <w:family w:val="modern"/>
+    <w:pitch w:val="fixed"/>
+    <w:embedRegular r:id="rId1"/>
+  </w:font>
+</w:fonts>`;
+}
+
+function fontTableRels(fontFilename) {
+  return `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
+  <Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/font" Target="${fontFilename}"/>
+</Relationships>`;
+}
+
+async function embedDocxFont(inputDocxPath, outputDocxPath, ttfPath, fontFamily) {
+  if (!ttfPath || !fs.existsSync(ttfPath)) {
+    throw new Error(`DocxFontEmbedder: TTF not found at ${ttfPath}`);
+  }
+  const inputBytes = fs.readFileSync(inputDocxPath);
+  const zip = await JSZip.loadAsync(inputBytes);
+  const safeFamily = String(fontFamily).replace(/[^A-Za-z0-9]/g, '');
+  const fontFilename = `${safeFamily}.ttf`;
+  const fontBytes = fs.readFileSync(ttfPath);
+  zip.file(`word/fonts/${fontFilename}`, fontBytes);
+  zip.file(FONT_TABLE_PATH, fontTableXml(safeFamily));
+  zip.file(FONT_TABLE_RELS_PATH, fontTableRels(fontFilename));
+  const out = await zip.generateAsync({ type: 'nodebuffer' });
+  fs.writeFileSync(outputDocxPath, out);
+}
+
+module.exports = { embedDocxFont };
diff --git a/tests/unit/main/monospace/DocxFontEmbedder.test.js b/tests/unit/main/monospace/DocxFontEmbedder.test.js
new file mode 100644
index 0000000..c52b93c
--- /dev/null
+++ b/tests/unit/main/monospace/DocxFontEmbedder.test.js
@@ -0,0 +1,65 @@
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+const JSZip = require('jszip');
+
+const { embedDocxFont } = require('../../../../src/main/DocxFontEmbedder');
+
+async function makeMinimalDocx(outPath) {
+  const zip = new JSZip();
+  zip.file(
+    '[Content_Types].xml',
+    '<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"></Types>'
+  );
+  zip.file(
+    '_rels/.rels',
+    '<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"></Relationships>'
+  );
+  zip.file('word/document.xml', '<w:document xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"/>');
+  const buf = await zip.generateAsync({ type: 'nodebuffer' });
+  fs.writeFileSync(outPath, buf);
+}
+
+describe('DocxFontEmbedder', () => {
+  let tmpDir;
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mono-docx-'));
+  });
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test('embeds TTF into word/fonts and updates rels', async () => {
+    const input = path.join(tmpDir, 'in.docx');
+    const output = path.join(tmpDir, 'out.docx');
+    const ttf = path.join(tmpDir, 'JetBrainsMono-Regular.ttf');
+    await makeMinimalDocx(input);
+    fs.writeFileSync(ttf, Buffer.from([0x01, 0x00, 0x00, 0x00, 0x00]));
+
+    await embedDocxFont(input, output, ttf, 'JetBrainsMono');
+
+    const result = await JSZip.loadAsync(fs.readFileSync(output));
+    const fontFiles = Object.keys(result.files).filter((n) => n.startsWith('word/fonts/'));
+    expect(fontFiles.length).toBeGreaterThan(0);
+    const rels = result.file('word/_rels/fontTable.xml.rels');
+    expect(rels).toBeTruthy();
+    const relsContent = await rels.async('string');
+    expect(relsContent).toContain('.ttf');
+  });
+
+  test('returns rejected promise for invalid docx input', async () => {
+    const input = path.join(tmpDir, 'invalid.docx');
+    const output = path.join(tmpDir, 'out.docx');
+    const ttf = path.join(tmpDir, 'JetBrainsMono-Regular.ttf');
+    fs.writeFileSync(input, Buffer.from('not a docx'));
+    fs.writeFileSync(ttf, Buffer.from([0x01]));
+    await expect(embedDocxFont(input, output, ttf, 'JetBrainsMono')).rejects.toThrow();
+  });
+
+  test('throws if ttf missing', async () => {
+    const input = path.join(tmpDir, 'in.docx');
+    const output = path.join(tmpDir, 'out.docx');
+    await makeMinimalDocx(input);
+    await expect(embedDocxFont(input, output, '/nope.ttf', 'JetBrainsMono')).rejects.toThrow(/TTF/);
+  });
+});