How to Compare Two Versions of a PDF and See What Changed
By Docmint Team · · 3 min read
Load the original and the revised PDF into a text comparison tool to see every added, removed or changed line. Here is how, and what it cannot catch.
To see what changed between two versions of a PDF, load both into a comparison tool that extracts the text and highlights the differences line by line. In Docmint's Compare PDFs, drop in the original and the revision: removed text shows in red and added text in green, page by page, and neither file is uploaded.
When does comparing PDFs matter?
The classic case is a contract. You send a draft, the other side sends back a "final" version, and you need to know whether anything changed beyond what was agreed. Reading two long documents side by side is slow and unreliable, because the eye slides over a changed number or a missing "not". A text comparison catches these mechanically.
The same applies to policies, terms of service, lease renewals, tender documents, papers between drafts and any report that went through several rounds of review. When a revision arrives as a PDF, the tracked changes from the word processor are usually gone, and comparison is how you get that information back.
How to compare two PDFs with Docmint
- Open Compare PDFs and drop in two files: the original and the revised version. Order does not matter, and you can swap them.
- Review the differences. Removed text is shown in red and added text in green, page by page.
- Use the arrows to jump from one change to the next, or filter the view to changed pages only.
- Turn on "Ignore whitespace changes" if the results are cluttered with differences that are only spacing or line wrapping.
- Download the comparison as a text or HTML report to share with colleagues or keep with your records.
How does a line-by-line text comparison work?
The tool extracts the text from each page of both PDFs and lines it up, much like the diff tools programmers use to compare versions of code. Lines that exist only in the original are marked as removed, lines that exist only in the revision are marked as added, and an edited line appears as a removal next to an addition, so you can read the old and new wording together.
Whitespace deserves a mention. If a document was re-exported with a slightly different font size or margin, lines can wrap at different words even though nothing was rewritten. Without the whitespace option, those rewrapped lines look like changes. With it on, you see only real edits to the words.
What will a PDF text comparison not catch?
Compare PDFs compares text. It does not detect changes to images, logos, signatures, charts, colors, fonts or bold and italic styling, or where elements sit on the page. A swapped photo, or a table moved to another spot with identical words, will not show up.
For visual checks, convert both versions with PDF to JPG and compare the page images by eye, flicking between them at the same zoom level. For scanned documents, run both files through OCR PDF first, because the comparison needs a text layer. With OCR output, expect occasional false differences where a character was recognized differently in each scan.
Can you compare more than two PDFs?
The tool works on exactly two documents at a time. If you have a chain of versions, compare them in pairs: version 1 against version 2, then version 2 against version 3. To see the total change from first draft to final, also compare the first draft directly against the final version.
Tips for reviewing contract revisions
- Compare the version you are about to sign against the last draft you agreed to, not against the very first draft. That isolates the late changes.
- Pay close attention to numbers, dates, defined terms and small words like "not", "may" and "shall", which change meaning without changing length much.
- Export the HTML report and keep it with the signed file as a record of what you reviewed.
- If a page shows no changes when you expected some, check that it actually contains text. A scanned signature page will look unchanged even when it is different.
- A comparison shows you what changed, not whether it matters. For significant agreements, have someone qualified review the substance.
Other ways to compare documents
If you still have the original Word or Google Docs files, their built-in compare features are excellent and also show formatting changes. Some desktop PDF editors include a compare function too. A browser-based text comparison is useful when all you have is two PDFs, when you do not have that software at hand, or when the documents are confidential and you would rather they stay on your machine.