Contract/PDF Redline Diff Viewer

See Contract/PDF Redline Diff Viewer in action

azrscorp.com/quickfix/pdf-document-diff-checker/

1Upload or drop the original document on the left.

2Upload or drop the revised document on the right.

3Click Compare and show redline.

PDF and Document Redline Diff Viewer — Compare Two Versions Instantly

When a contract, policy or report goes through several drafts, finding exactly what changed between two versions by eye is slow and risky — a single deleted clause or changed number is easy to miss. This tool takes two documents, the original and the revised version, extracts their text and shows a redline: every word that was added appears highlighted in green, and every word that was removed appears struck through in red, exactly like the markup a lawyer or editor would produce by hand.

It accepts PDF, plain text (.txt) and Word (.docx) files in any combination — extracting PDF text with pdf.js and .docx text with mammoth.js, the same libraries already used elsewhere on this site. The comparison itself runs a word-level (or, if you prefer, line-level) diff algorithm entirely in your browser, so contracts and sensitive documents never leave your device. A summary shows how many words were added, how many were removed, and an overall similarity percentage, so you can gauge at a glance how heavily a document was revised before reading the detail.

Key features

How to use it

1. Upload or drop the original document on the left.
2. Upload or drop the revised document on the right.
3. Click Compare and show redline.
4. Review the green additions and red deletions, and check the similarity score.

Worked example

Example

Clause 4.2 changes from “the deposit is refundable within 30 days” to “the deposit is non-refundable” → the redline shows “refundable” struck through in red and “non-refundable” inserted in green, so the change is impossible to miss.

Who uses this tool

Tips for the best results

• Use word-level diff for contracts and precise wording; switch to line-level for restructured documents where whole paragraphs moved.
• Check the similarity percentage first — a very low score usually means the documents are different files entirely, not just revised.
• For scanned (image-only) PDFs, text extraction will return little or nothing — use a text-based or OCR'd PDF instead.
• Keep both original files handy in case you need to double-check formatting the plain-text diff cannot show.

Common mistakes to avoid

• Comparing a scanned image PDF, which has no extractable text layer.
• Assuming the diff shows formatting changes — it compares the words only, not fonts, styles or layout.
• Reading only the summary numbers without checking the actual redline for context around each change.

Frequently asked questions