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What Compare PDF does
Compare PDF extracts the text of two PDFs and diffs them line by line, highlighting exactly what was added and removed between the original and the changed file.
When you have two versions of a contract, a report or a spec, the question is usually simple: what actually changed in the wording? Compare PDF answers that by pulling the real text out of both files and running a line-by-line diff, so edits stand out instead of being hunted for.
Both PDFs are read in the browser with pdf.js and compared with a standard diff, the same kind that powers code review. Added lines are marked in green, removed lines in red, and unchanged text is dimmed — with a count of how much changed. Nothing is uploaded; both files stay on your device.
How to use Compare PDF
Add both PDFs
Drop the original on the left and the changed version on the right. Both must be text-based — OCR a scan first.
Compare
Click Compare PDFs. The text of each is extracted and the two are diffed.
Read the differences
Additions and removals are highlighted inline with a summary of how many lines changed.
Compare PDF: details and limits
This compares text, not appearance. Layout, fonts, colours, images and positioning are not diffed — only the words. Two PDFs that look different but read the same will report no differences.
The diff is line by line, so a moved paragraph shows as a removal in its old place and an addition in its new one, even though the words did not change.
Both files need a real text layer. A scanned PDF has nothing to compare, so OCR it first; password-protected files must be unlocked first. Each file is named in any error so you know which one to fix.