Find what changed between two versions
Someone sent back “the contract, lightly edited.” Lightly, sure. Now you’re squinting at two near-identical PDFs trying to find the three words they quietly changed. This does that squinting for you. Drop in the original and the new version, and every added line shows up green, every removed line red, the rest stays put.
It works like a code diff, just for PDF text. Two documents go in. A line-by-line comparison comes out, with a running count of how many lines were added and removed. If nothing changed, it says so outright instead of making you scroll to be sure.
How the comparison runs
Both files stay on your machine. The tool pulls the text out of each PDF right in the browser using pdf.js, lines them up with a longest-common-subsequence diff (the same approach Git uses), and paints the result. No upload, no server, no copy of your contract sitting in someone’s queue.
Toggle “Show only changes” to hide the lines that match and focus on the edits. Leave it off to read the whole document with the changes in context. For long files, the comparison caps at the first 2500 lines per side so a giant PDF can’t lock up your tab, and it tells you when that cap kicks in.
What it compares, and what it doesn’t
Be clear on this part. It compares text, not layout. Font changes, a moved logo, a resized table, a swapped image: none of that shows up, because the words are identical. What you get is a precise read on content edits, the stuff that actually changes meaning in a contract, a policy, or a manuscript.
One hard limit: the PDF needs real, selectable text. A scanned document is just a picture of text as far as a computer is concerned, so there’s nothing to extract and nothing to diff. Run it through OCR first if you’re working with scans.
Where it earns its place
- Contracts and agreements going back and forth in redlines, when you need to catch every edit
- Comparing two drafts of a report, proposal, or thesis chapter
- Checking a resigned or re-exported PDF against the original to confirm nothing shifted
- Policy and documentation updates where you need a record of what changed between revisions
Questions people ask
Does it upload my PDFs anywhere? No. Text extraction and the diff both happen in your browser. The files never leave your device, which makes it safe for confidential or legal documents.
Why does it say “no selectable text”? That PDF is almost certainly a scan, an image of a page rather than real text. There’s nothing to compare until you OCR it into actual characters first.
Will it show formatting or image differences? No. It compares the words only. Two pages with identical text but different fonts or layout will read as a perfect match.
My documents are huge. Will it handle them? Up to a point. It compares the first 2500 lines of each file and warns you if it had to stop there. For very large PDFs, compare the relevant sections separately.
Can I download the diff? Not as a file yet. You can select the highlighted result and copy it, or screenshot the section you need.
Does the order of the two files matter? A little. The left slot is treated as the original and the right as the changed version, so “added” and “removed” are relative to that. Swap them and the colors flip.