How to compare two PDFs on a Mac
By Himanshu Ranjan · Updated 8 November 2026
To compare two PDFs on a Mac, select both in Finder and run Combine › Compare two PDFs in FileDial. It writes a report PDF with removed text in red and added text in green, side by side. It runs offline, so contracts and drafts are never uploaded.
What a PDF comparison tells you
When a contract comes back from the other side as a new PDF with no tracked changes, you need to know what moved. Reading two 30-page files side by side is slow and easy to get wrong, because a single changed number is invisible among a thousand unchanged words.
FileDial's Combine › Compare two PDFs produces a report PDF in which removed text is red and added text is green, shown side by side. That turns an hour of reading into a few minutes of checking the colored parts.
Compare two versions with FileDial
Select exactly two PDFs, and choose which is the older version.
- In Finder, select the two PDFs, the old version first.
- Hold the right Option key to open the dial and choose the Combine category.
- Release on Combine › Compare two PDFs.
- Open the report PDF and scan for red and green passages.
- Read each change in context against the original pages before accepting or objecting.
Reading the report
Red means text that was in the first file and is not in the second. Green means text that is in the second and not in the first. A changed number appears as a red number next to a green one. A paragraph moved from page 4 to page 9 appears as a deletion in one place and an addition in another, so a lot of color does not always mean a lot of change.
Look especially for small edits with large effect: amounts, dates, party names, the word not, and defined terms. Those are the changes that matter, and they are the ones that are easiest to miss by eye.
- Red: only in the first PDF.
- Green: only in the second PDF.
- Moved text shows as both.
- Pay most attention to numbers, dates and names.
What a text comparison cannot see
The report compares text. A changed image, logo, signature or chart is not text, so a swapped picture or a redrawn table that is an image may not show up. Formatting changes such as font or margins are also not the point of a text diff. If the PDFs are scans, the text must be read by OCR first; run OCR › Make searchable on each, or the comparison has nothing to compare, and OCR errors will appear as differences that are not real.
Treat the report as a strong aid, not a guarantee. For a high-stakes contract, still read the final version in full.
Comparisons are best between two PDFs produced the same way. A Word export compared with a scan of a printout gives noise from every OCR mistake. If you can, ask for both versions in the same format, or convert both to searchable PDFs the same way. Strip page numbers or headers that change on every page by working on copies if they swamp the report.
If one file has extra cover pages, use Organize › Delete pages… on a copy so that pages line up.
A worked example: a lease renewal
The landlord sends lease-renewal.pdf and says only some small changes. Select last year's lease first and the new one second, run Compare two PDFs, and open the report. You see rent raised in red and green, a notice period changed from 30 to 60 days, and a new paragraph about pets in green. Those three items are what you discuss; the rest is unchanged.
Take the report's pages as a checklist: for each colored passage, write a line saying accept or ask. Then send the questions rather than the PDF. Keep the report with the two versions in one folder named for the date, so that months later you can show exactly what changed and when.
Common mistakes
Selecting the files in the wrong order swaps red and green, so the story reads backwards. Check which is which on the first page of the report. Comparing a scan with a digital file creates false differences; fix the inputs first. Skimming only the first pages is another trap, since edits cluster near definitions and schedules at the end. And do not paste a comparison into an email as proof without checking the colored parts against the source pages; it is a tool for reading, not evidence on its own.
Honest alternatives on a Mac
Word has its own Compare feature for Word documents, and some editors can diff text files, but those need the source files. When all you have are two PDFs, a PDF comparison is the right tool. Preview has no comparison feature we can point you to; you can open two windows side by side and read, which is fine for a page or two.
The documents people compare are often unsigned contracts, legal drafts and financial terms. They are the files not to upload to a free site. FileDial compares on your Mac with Wi-Fi off and writes the report beside your files.
Questions
Can I compare two PDFs for free on a Mac?
You can open both in Preview side by side and read them, which suits a page or two. For a whole document, FileDial's Combine › Compare two PDFs gives a report with removed text in red and added text in green, run on your Mac.
Does it compare images and layout?
The report is about text, so a changed image, logo or layout may not appear in it. If the PDFs are scans, run OCR first so there is text to compare. For important documents, still read the final version yourself. Check the result before relying on it.
Why does my comparison show differences that look identical?
Small differences such as spacing, line breaks, hyphenation or OCR misreads can register as changes. Compare PDFs created the same way, and OCR scans the same way. Check each flagged passage in context before deciding it is a real change. Check the result before relying on it.