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Can you track changes in a PDF? What works instead on a Mac

2026-10-30 · can you track changes in a pdf

No, you can't track changes in a PDF the way a word processor does. A PDF has no revision log, no accept or reject buttons and no record of who changed which word. What you can do is mark it up with comments, compare two versions, or rely on a digital signature to tell you whether it changed after signing.

The surprise runs the other way, too. People ask how to see tracked changes in a PDF because they were sent a document with them, or they worry that their own file shows edits they meant to accept. The markup that leaks often comes from the word processor, before the PDF existed.

Why a PDF can't track changes

A word processor stores a document as a flow of text with a list of edits laid over it, so each insertion and deletion can be named, dated and reversed. A PDF stores finished pages. It records where glyphs are drawn, not how they got there.

Some PDFs do keep earlier states. When a program saves by appending, the old bytes stay in the file and a new section is added after them. That's an incremental update. It isn't a change log: nothing in it says what changed, who changed it or why, and a file written in one pass has none. Incremental saves and what they leave behind covers what that means for privacy.

A linearized file, which is optimized for fast web view, can also show more than one saved generation with no edits at all. So an earlier state in the file is a hint, never a history.

Comments and markup are the closest feature

The nearest thing to tracking in a PDF is annotation. Reviewers add highlights, notes, strikethroughs and text boxes, and each one is stored as an object on the page with its own text, position and, usually, an author and a date.

In Preview, click the Show Markup Toolbar button if the Markup toolbar isn't showing. Apple's Preview guide presents these tools for exactly this: use them "to suggest changes to a PDF and to respond to suggestions." Highlights, strikethroughs and notes suggest a change. They don't make one, and the text underneath stays as it was until somebody edits the source.

To see who marked what, choose Tools > Show Inspector and open the Annotations pane. It lists each annotation with its type, author, date and page. Remember the reverse risk: the author stored with a comment is a name, and it travels with the file. What a PDF annotation is explains the fields and why an annotation sometimes doesn't show.

When tracked changes come along from the word processor

If your PDF came from a word processor, the real question is often what the export did with the markup. Depending on the program and its settings, exporting while changes are showing can print the revisions into the page as colored text, or carry comments along as annotations. Exporting with markup hidden prints the clean version.

Check before you send. Open the PDF and look for colored, struck-through or underlined text and for comment balloons or notes in the margin. Open the Annotations pane in Preview's Inspector and see whether it lists comments you didn't add on purpose. If either is there, go back to the source document, accept or reject the changes, delete the comments and export again.

Do the same for a document you've received as a PDF and want to answer. If the sender's edits are drawn into the page, the original wording is often still readable in them. Redacting a word processor document converted to PDF goes through the leak in more detail.

Comparing two versions

When you have the old and the new file, comparing them is the substitute for a change log. A text comparison is the practical choice, since it ignores where things sit on the page.

On a Mac you can do a rough comparison in Terminal. Each command writes a text file with one line per line of extracted text, and then diff shows what's different between them. Use your own file names:

mdimport -t -d3 old.pdf | grep kMDItemTextContent | sed 's/\\n/\
/g' > old.txt
mdimport -t -d3 new.pdf | grep kMDItemTextContent | sed 's/\\n/\
/g' > new.txt
diff old.txt new.txt

With two sample files that differed in one line, the output showed that line and nothing else. It's text only, and it will show every re-wrapped line as a change if the layout moved. Comparing two PDFs and comparing contract versions cover the options for a longer document.

What a signature can and can't tell you

A digital signature covers the file as it was when it was signed. A reader that checks signatures can tell you whether the file changed afterward. It can't tell you what changed.

Signatures rely on incremental updates: later changes are appended after the signed bytes, which is how a reader can see that something was added. A valid signature proves integrity from the moment of signing and says nothing about the time before it. If you must know what differs, compare the signed copy with the one you were given.

This means a certificate-based digital signature. Preview's Sign button is something else: it places a signature you drew or photographed on the page, which records nothing about later changes.

What to do on a Mac in practice

Pick the approach that matches your goal.

• Reviewing someone else's draft. Use comments in Preview, and send back the annotated copy.
• Needing a record of edits. Keep the document in the word processor, where tracking exists, and export a PDF at each stage. Name them in order.
• Checking what changed between two PDFs. Compare them as text.
• Needing proof of what was agreed. Sign the final file with a digital signature and keep the signed copy.