How to compare two PDFs and see what changed between versions

How to compare two PDFs and see what changed

To compare two PDFs, upload the old file first and the new one second. The comparison starts on its own and shows a summary ("X of N pages have differences") plus a page selector with the percentage that changed on each one. In "Text" mode, added words appear in green and removed words in red strikethrough; in "Image" mode, the areas that changed are painted over the page. Nothing is downloaded: the result is meant to be viewed on screen, in your browser.

What the tool does (and what it doesn't)

• Compares exactly two files: the first one uploaded is treated as "old" and the second as "new". If you upload more, you'll see "Comparing the first two uploaded files."
• Compares page by position: page 1 against page 1, 2 against 2, and so on. Pages that exist in only one file get the "only in one" label.
• Four ways to view each page: "Text" (word-by-word difference in a text box), "Image" (a visual map of what changed, painted over the page), "Old" and "New" (the page from each file). One panel at a time; there's no side-by-side view.
• On a page with no text (scanned), "Text" mode automatically falls back to "Image".
• No report and no annotated PDF: there's no download button. To keep evidence, take a screenshot.

When comparing versions really matters

• Contract review: check whether the other party changed a clause, a deadline or a figure before you sign.
• New vs. old version: find out what a colleague edited in a document that came back revised.
• Proposals and quotes: compare what changed between the first and second round of negotiation.
• Official documents: verify whether a re-sent file is really identical to the one you approved.

Step by step to compare the two files

1. Open the compare PDF tool.
2. Upload the two versions in this order: the old file first, then the new one. The comparison starts on its own. The screen confirms the order in a line showing each file name followed by "(old)" and "(new)".
3. Read the summary ("X of N pages have differences" or "No differences found — the documents are identical.") and use the "Page" selector to jump straight to the pages marked with a percentage.
4. Switch between "Text", "Image", "Old" and "New" to understand each change.

How to read the result

• The summary line tells you how many pages changed. The message "No differences found — the documents are identical." means the two files match page for page. Tiny changes, under 0.1% of the page, count as identical.
• In the "Page" selector, each changed page carries the percentage that changed (for example, "Page 3 • 2.4%"); identical pages show no mark, and pages present in only one file carry the "only in one" label. Above the page you see "X% of the page changed." or "This page is the same in both."
• In "Text" mode, the legend "added" (green) and "removed" (red strikethrough) explains the colors. When only the layout changed, you'll see "The text on this page is the same in both files." Switch to "Image" to see the visual difference.
• For a page that exists in only one version, the tool says "This page exists only in the old file." or "…only in the new file." and shows that page.

Text or Image: which mode to use

For two text PDFs (made in Word, a business system, an editor), use "Text" mode: it shows exactly which words came in and went out, and it's the only mode that tells additions from removals. For scanned documents, use "Image" mode, which compares the drawing of the page dot by dot and paints what changed, without saying whether it was added or removed. Mixing a scan with a text PDF only works in "Image" mode, and small scanning differences (tilt, brightness) can show up as changes. If one of the versions asks for a password, the comparison cannot open it: first, see how to remove a password from a PDF.

Common errors and limits

• Wrong order: if the new file went in first, green and red are reversed. Remove the files and upload them again in the right order.
• A page inserted in the middle: since the comparison is by position, every following page is shifted and shows up as different. In that case, check the matching pages in "Old" and "New" modes.
• A document scanned twice: even with no change in content, "Image" mode may flag differences caused by the scanning itself.
• Pages of different sizes (A4 in one file, letter in the other): "Image" mode lines the two up by the top-left corner, and the extra area of one of them counts as a difference.
• Password-protected PDF: the comparison can't open the file and shows "Couldn't compare the PDFs." Remove the password first, with the unlock tool.
• Large files: the pages are rendered on your device; with PDFs of hundreds of pages, the comparison can take a few moments.

Everything happens on your device: both PDFs are compared in your browser and never sent to any server, which is essential for contracts and confidential documents.