PDF Diff & Comparison Tool
Upload two PDF files to compare their text content — mismatches, additions, and removals highlighted word-by-word.
Free PDF Comparison Tool — Word-Level Diff, No Upload
This free PDF diff tool extracts text from two PDF files and compares them word-by-word and line-by-line — entirely inside your browser. It uses the open-source PDF.js library for text extraction and a Longest Common Subsequence (LCS) algorithm for precise word-level diffing. Your files are never uploaded to any server — nothing leaves your device.
The result is a detailed comparison showing every addition, removal, and change — with individual changed words highlighted in green and red, not just entire lines. A similarity score tells you at a glance how alike the two documents are, and you can toggle between side-by-side and unified views depending on how you prefer to review changes.
What This PDF Diff Tool Can Do
- Word-level highlighting — Changed words are highlighted individually using an LCS algorithm, not just entire lines. Additions appear in green, removals in red with strikethrough.
- Side-by-side view — Both PDFs displayed in parallel columns for quick scanning of corresponding sections.
- Unified view — All changes shown in a single column with old/new labels — useful for sequential review of every modification.
- Similarity score — Instant percentage showing how alike the two PDFs are, calculated from unchanged vs total lines.
- Change summary — Count of unchanged, changed, added, and removed lines displayed before the diff results.
- Show/hide unchanged lines — Focus only on differences, or toggle to see full document content.
- 100% private — PDF text is extracted locally in your browser using PDF.js. No file upload, no server, no account.
Who Uses a PDF Comparison Tool?
Lawyers and paralegals comparing contract revisions to find clause changes between draft versions. Academics comparing two versions of a research paper before and after peer review. Procurement teams reviewing supplier agreement updates. HR departments checking whether a policy document was changed before re-signing. Developers comparing exported PDF reports from two software versions to verify output consistency.
This tool is particularly useful as a free alternative to Adobe Acrobat's Compare Documents feature or tools like Draftable — with the added advantage that nothing is uploaded to a third-party server, making it safe for confidential documents like contracts, legal filings, and HR records.
Need to convert an image to PDF first? Use the Image to PDF Converter. Working with JSON data instead? The JSON Formatter & Diff tool compares JSON objects the same way — instant, private, no upload.
Frequently Asked Questions
What kinds of PDFs can I compare?
This tool works best with text-based PDFs — documents created in Word, Google Docs, or exported from web pages. Scanned PDFs (image-only) contain no embedded text and will show empty results. For scanned documents, you would need OCR software to extract text first.
Is my PDF uploaded to a server?
No. PDF text extraction runs entirely in your browser using the open-source PDF.js library. Your files never leave your device — making it safe for confidential documents.
Why does the comparison show false differences?
PDFs encode text in visual order (page position), not logical reading order. If a paragraph reflows between versions, lines may shift even if the content is identical. This is a limitation of PDF text extraction, not the diff algorithm.
What does the similarity score mean?
The similarity percentage is the proportion of unchanged lines relative to the total number of lines across both documents. A score of 100% means the extracted text is identical.
Can I compare large PDFs?
Yes. For very large PDFs (100+ pages), extraction may take a few seconds depending on your device. The diff itself runs quickly even for thousands of lines.
What is the difference between side-by-side and unified view?
Side-by-side shows both PDFs in parallel columns for quick scanning. Unified view shows all changes in a single column with old/new labels — useful for a sequential review of every modification.
Is this a free alternative to Adobe Acrobat Compare Documents?
Yes. Adobe Acrobat's comparison feature requires a paid subscription. This tool does word-level PDF comparison completely free — no account, no upload, no file size limit, and your documents stay on your device.