Compare PDFs
Line up two PDFs page by page and find what changed, visually and in the text. Runs in your browser with no upload.
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Compare PDFs: complete guide
Walk through the steps and examples, or jump straight to the topic you need.
At a glance
- What you add
- Two PDFs. The left one is the earlier document and the right one is the later document.
- How pages are matched
- Page 1 is compared with page 1, page 2 with page 2, and so on in page order.
- Visual comparison
- Both pages are drawn at the same size, the pixels with different colors are counted, and a mark is overlaid on those spots.
- Text comparison
- The text in each document is extracted, and the changed, added and removed lines are counted.
- Verdict
- If even one character changes, the page is different. Only when the text is unchanged are pixels used: no differing pixels means identical, under 0.05% means nearly identical, and anything more means different.
- Tolerance
- Set the color difference from 0 to 255. The default is 16.
- Limits
- 60 MB per file and up to 300 pages per document.
- Where it runs
- Everything from reading the files to comparing them happens inside this browser.
How to use Compare PDFs
Add the two documents
Put the earlier document on the left and the later document on the right. Once added, each document's page count and size are shown, and you are warned in advance if the page counts differ.
Adjust the tolerance if needed
At the default of 16, differences like print density are ignored. Lower the value to find even very small differences, or raise it for scans with lots of specks.
Click Compare
It compares page by page and shows its progress. If it takes too long, you can stop it, and your files stay loaded.
Start with the different pages
When the results appear, the first different page is already selected. Use the next-different-page button to step through, and check the marked spots with both originals side by side.
What it’s good for
It first finds which pages changed
The two documents are laid side by side in page order, and each page is marked as identical, nearly identical or different. If even one character changes, the page is reported as different, however small the visual change is. You can jump straight through the different pages only, so you can find what changed quickly even in a long contract or proposal. If the page counts differ, the extra pages are reported as present in only one document.
It looks at both a visual comparison and a text comparison
The visual comparison draws both pages at the same size, counts the pixels whose colors differ, and overlays a mark on those spots. It also catches non-text changes such as a stamp or a table line. The text comparison pulls out the text in each document and counts the changed, added and removed lines. Looking at both lets you tell visible changes apart from changes in content.
What this method cannot tell you
In a document scanned as a photo, the text is stored as an image, so a text comparison is not possible and you only get the visual result. If a document does not embed its fonts and a substitute font is drawn instead, pages with the same content can look different on screen. Also, the tool does not automatically realign pages that shifted wholesale or were reordered, so in that case check by hand from the point where the page numbers start to go out of step.
Worked examples
A quote where only an amount was changed
Earlier 3 pages · Later 3 pages · Tolerance 16Different pages 1 · Identical pages 2 (3 pages total)
Page 2 text comparison: changed lines 1A document with extra pages at the end
Earlier 5 pages · Later 7 pagesIdentical pages 5 · Only on the right 2 (7 pages total)Choosing a tolerance
Swipe the table sideways to see the rest.
| Value | Good for | Keep in mind |
|---|---|---|
| 0-5 | Finding very small differences between files made identically | Even a slight difference in compression gets flagged as different. |
| 16 (default) | Comparing versions of an ordinary document | Ignores slight density differences and still catches visible changes. |
| 40 or more | Documents with lots of specks, such as scans | Faint text changes can be missed. |
When the result isn’t what you expected
Every page shows as different even though the content is the same
If a document does not embed its fonts, the browser draws a substitute font and the letter shapes drift slightly. In that case, look at the changed-lines count in the text comparison rather than the visual comparison. If changed lines is 0, the content is the same.
No text comparison appears
In a document scanned as a photo, the text is stored as an image, so there is no text to extract. Only the visual comparison appears. If you want to convert it to text, run it through image text extraction (OCR) first.
I cannot tell where the pages started to go out of step
In the page list, the point where a run of identical pages turns into different pages is where things started to drift. Put the two originals of that page side by side to tell whether a page was inserted or the content was edited.
The comparison takes a long time
It draws both documents for every page and compares them, so many pages take time. Click Stop to halt it right away. To compare only the pages you need, split the documents with the PDF split tool first and then add them here.
Key terms
- Pixel
- The smallest dot that makes up the screen. The visual comparison compares the colors of these dots one by one.
- Tolerance
- The value that sets how different two colors must be before they count as different.
- Nearly identical
- The text is unchanged, and only under 0.05% of the pixels differ. That is a difference on the order of a single dot.
Compare PDFs FAQ
Can I compare documents with different page counts?
Yes. Pages are matched in order from the start, and any extra pages are marked as present in only one document. However, if a page is inserted in the middle, everything after it shifts by one and looks different, so check by hand from the point where it goes out of step.
What is the color difference tolerance?
It sets how different two colors must be before they count as different. Enter a value from 0 to 255; the default is 16. Raising it ignores slight variations such as differences in print density, and lowering it catches even very small differences.
Are my documents uploaded to a server?
No. Reading the files, drawing the pages and comparing them all happen inside this browser.
Can it compare a scanned contract?
The visual comparison works. However, the text is stored as an image, so a text comparison is not possible. Even a slight difference in scan quality or tilt can show up as large differences in the visual comparison, so check the marked spots with your own eyes.
Does it show in words which page changed and how?
It counts the changed, added and removed lines. To see them line by line side by side, extracting the text and using a text comparison tool gives more detail.
Does it work with password-protected PDFs?
A document that asks for a password to open cannot be opened, and the tool tells you why. Remove the password first, then add the file.
Can I save the comparison result as a file?
For now, you can only review it on screen. Exporting the result to a file is not included.