How to Compare Two PDF Files and See Exactly What Changed

A contract comes back with “just a few small edits”. A supplier sends a new price list. The designer delivers version 7 of the brochure. In every case the question is the same: what exactly changed? Reading both versions side by side takes ages, and the one changed number is easy to miss.

This guide shows how to find every difference between two PDFs in a minute with the free Compare PDF Files tool, and which kind of comparison to use when.

Two ways to compare a PDF

A PDF holds two things: the text, and how each page looks. The tool compares both.

• Text comparison reads the words in both files and lines them up. It finds changed sentences, numbers, names and dates, even when a paragraph has moved to another page because something was added before it.
• Visual comparison draws each page as a picture and compares the pictures. It finds what text can’t show: a new logo, a moved image, another colour, a different layout or a signature that was added.

For contracts and reports, the text comparison is the one to read. For brochures, forms and designs, look at the visual comparison too.

How to compare two PDFs

1. Open Compare PDF Files. Drop the older file on Original PDF and the newer one on Changed PDF, or click choose a file. You see each file’s pages and details, such as its title, author and the date it was changed.
2. Click Compare PDFs. Long documents are read one page at a time with a progress bar, and Cancel stops at any moment.
3. Read the summary at the top: the number of Text changes, words added and removed, and Pages that look different.

Reading the text comparison

Both documents are shown side by side. Words that were added are green, words that were removed are red, and words that were changed are amber. Use ‹ Previous and Next › to jump from one change to the next: both sides scroll to it together, so you never lose your place.

If only capital letters changed (for example a heading changed from “Payment terms” to “Payment Terms”) and that doesn’t matter to you, tick Ignore upper and lower case.

Using the visual comparison

Open Visual comparison to see the pages themselves, with the areas that look different boxed in red. The list of Changed pages takes you straight to the pages that matter. Three views help you see what happened:

• Side by side: both pages next to each other. Turn pages together keeps them in step.
• Overlay: one page on top of the other, so anything that moved even slightly stands out.
• Differences only: the page faded to grey with every changed pixel in red, which makes tiny edits easy to spot.

Sensitivity decides how big a difference must be to count. Raise it to catch the smallest change; lower it if a file was saved with a different program and every page shows tiny differences in the edges of letters. Highlight and Zoom help with detailed pages.

Save a report

Click Download report (PDF) to keep the result or send it to someone. The report lists both files and their details, a summary, every text change as before and after with its page number, and the pages that look different side by side with the changes marked.

Password-protected, large and scanned PDFs

• Protected PDFs: type the password when asked. It is only used in your browser to open the file.
• Long documents: pages are read and drawn one at a time, so a 300-page report works too; it just takes a little longer.
• Scanned PDFs: a scanned page is a picture with no text, so there is nothing for the text comparison to read. The tool tells you when a file looks scanned; the visual comparison still works. To get the text of a scanned page, take a screenshot of it and use Image to Text.

Are my PDFs uploaded?

No. Both files are read, compared and drawn inside your browser, so they never leave your device. That matters for contracts, invoices and anything confidential.

Frequently asked questions

Can I compare a Word document with a PDF?

Save the Word document as a PDF first (File, Save as, PDF), then compare the two PDFs. To compare plain text or code files, use File Comparison.

Why does every page look different?

Usually because one file was made with another program or at another size, which shifts every letter by a pixel. Lower the Sensitivity, and rely on the text comparison for the actual wording.

What if a page was added in the middle?

The text comparison handles it: it shows the new text as added and keeps matching the rest, even though everything after it moved to a later page.