Compare PDF Files
Compare two versions of a document. The text comparison tells you which lines changed; the optional appearance comparison catches the changes text cannot see.
First file
Second file
Runs entirely in your browser. Your files are never uploaded.
How to use Compare PDF Files
- 1Choose the original and the revision.
- 2Tick the appearance option if layout or images matter, not just wording.
- 3Press Compare files.
- 4Read the per-page results and the lines that differ.
Two questions, answered separately
Has the wording changed is answered by pulling the text out of both documents and comparing it line by line. That is reliable when both files have a text layer, and worthless when either is a scan, so the tool says when it suspects that rather than reporting a confident nonsense.
Does the page look different is a separate question, answered by rendering both pages and counting pixels that disagree. It catches a moved logo, a changed chart, a different font. It also flags changes nobody cares about, which is why it is off until you ask for it: it is slower, and it is noisier.
What the percentages mean
The text figure is the proportion of lines the two pages share. Lines are compared as whole lines, so changing one word in a sentence marks the whole line as different. The lines themselves are listed, so you can see what actually moved.
The pixel figure is the proportion of the rendered page that differs, with a tolerance for anti-aliasing. Anything under about half a per cent is usually noise. A few per cent is a real but localised change. Twenty per cent is a different page.
Where it falls down
Pages are matched by number. Insert a page near the front and every page after it reads as changed, because page four of the original is now page five. That is accurate and almost never what you meant. There is no realignment, because a comparison tool that silently guesses the wrong alignment is harder to catch out than one that is obviously offset.
Line comparison also has no sense of order, so two paragraphs swapped on a page score as identical. For the question people usually have, which is whether anything was edited, that is the right answer. For reviewing a restructure, it is not.
This is not a legal diff. It will not tell you a clause changed meaning, and it should not be the only check on a contract.
Limits
- 100 MB per file.
- Password-protected PDFs need unlocking first.
- Pages are matched by position, not by content.
- Text comparison works on whole lines, not words.
- Scanned documents have no text to compare; use the appearance option.
- Comparing appearance renders both files, which is slow on long documents.
Frequently asked questions
- Can it show me exactly which words changed?
- It shows which lines differ, side by side, rather than highlighting individual words. For a changed sentence you will see both versions of the line and can read the difference.
- Why is every page after page 3 marked as changed?
- Almost certainly a page was inserted or deleted near the front, so the pages no longer line up by number. Compare the sections either side of the insertion separately.
- It says there are no text differences, but the pages look different.
- Then the change is in layout, images or fonts rather than wording. Tick the appearance option and compare again.
- Can I compare two scans?
- Only by appearance. Scans have no text layer, so there is nothing for the text comparison to read, and the tool tells you when it sees that.