How to Annotate PDF Files: A Complete Guide to Comments and Markups

I watched a colleague print out a 40-page contract, read through it with a red pen, scan all the pages back in, and email the scanned marked-up version to the client. The whole process took over an hour. The scanned pages were crooked, some annotations were cut off, and the file size was enormous because it was basically 40 photos.

"Why didn't you just annotate the PDF directly?" I asked.

He looked at me like I'd suggested magic. "Can you do that?"

Yes. Yes you can. And you should. PDF annotation has been a standard feature for decades, yet somehow people still don't know it's an option. Let me fix that.

What Is PDF Annotation?

PDF annotation is adding comments, highlights, drawings, and notes directly to a PDF file without changing the underlying content. Think of it like writing in the margins of a book, except digital — cleaner, searchable, and easy to remove if needed.

Annotations live as a separate layer on top of the document. You can show them, hide them, edit them, or delete them without touching the original content. This makes them perfect for review cycles, collaborative editing, and personal note-taking.

Types of PDF Annotations

Different tools offer different annotation types, but these are the most common:

Text Highlights and Underlines

The digital equivalent of a highlighter pen. Select text and apply yellow highlight, underline, strikethrough, or squiggly underline. Most tools let you change the highlight color — useful for color-coding different types of information.

Sticky Notes and Comments

Click anywhere on the page and add a text comment. These show up as little icons that expand when clicked. You can write as much as you want — paragraphs if needed — without cluttering the document.

Freehand Drawing

Draw circles, arrows, lines, or freeform doodles directly on the page. Great for calling attention to specific areas, drawing attention to design elements, or sketching quick diagrams.

Text Boxes and Callouts

Add standalone text anywhere on the page. Unlike sticky notes, this text is always visible. Callouts include a line pointing to a specific area — perfect for labeling diagrams or images.

Shapes and Stamps

Rectangles, circles, arrows, lines. Some tools include stamp libraries with common marks like "APPROVED," "DRAFT," or "CONFIDENTIAL." You can also create custom stamps with your own text or images.

Attachments and Audio

Advanced annotation features let you attach files or record audio notes directly to the PDF. These are less common but incredibly useful for detailed reviews.

Why Annotate Instead of Edit?

You might wonder: why add annotations instead of just editing the PDF directly? Great question.

Preservation of Original Content

Annotations don't change the underlying document. If you're reviewing someone else's work, annotations let you suggest changes without altering their file. They can accept or reject your feedback as they see fit.

Non-Destructive Workflow

Made a mistake in your annotation? Just delete it. Change your mind about a suggestion? Edit the comment. With direct editing, changes are permanent unless you keep multiple file versions.

Review Cycles

Annotations are designed for feedback. Multiple people can add their comments, reply to each other's notes, and track the status of suggestions. Most annotation tools show who made which comment and when.

Legal and Compliance

In regulated industries, keeping the original document intact is often required. Annotations provide a clear audit trail of what was suggested versus what was actually in the original file.

How to Annotate PDFs: Your Options

Option 1: Browser-Based Tools

The most accessible option. Our PDF annotation tool runs entirely in your browser. Upload your PDF, add your marks, download the annotated version.

Browser-based annotation has come a long way. Modern tools support:

• Text highlighting in multiple colors
• Sticky notes and comments
• Freehand drawing with adjustable pen sizes
• Shape tools (rectangles, circles, arrows)
• Text boxes and callouts

The key advantage is privacy. Tools like PeacefulPDF process everything locally in your browser. Your document never uploads to a server, which matters when you're annotating confidential or sensitive files.

Option 2: Adobe Acrobat Reader (Free)

The free version of Acrobat Reader lets you add sticky notes, highlights, and basic markup. It's limited compared to the Pro version — you can't edit existing text or add complex annotations — but for simple markup, it works fine.

To annotate in Reader, look for the "Comment" tool in the right sidebar. You'll get a toolbar with highlighting, sticky notes, and drawing tools.

The catch? Acrobat Reader annotations sometimes don't display correctly in other PDF viewers. If you're sharing annotated files, test them in the recipient's preferred viewer.

Option 3: Preview on Mac

Preview has surprisingly good annotation capabilities. Click the markup toolbar icon (looks like a pencil tip) to access:

• Text selection and highlighting
• Rectangular and elliptical shapes
• Lines and arrows
• Freehand sketching
• Text boxes
• Signatures

Preview's annotation tools are straightforward and work well for most tasks. The annotations are standard PDF annotations, so they display correctly in other viewers.

Option 4: Microsoft Edge

If you're on Windows, Microsoft Edge has built-in PDF annotation. Open a PDF in Edge, click the "Add notes" button in the toolbar, and you can highlight text and add ink annotations.

It's basic — no sticky notes, limited drawing tools — but it's convenient if you just need to quickly mark up a PDF without installing anything.

Option 5: Mobile Apps

For annotating on phones and tablets, there are dozens of apps available. Adobe Acrobat Reader mobile, PDF Expert (iOS), Xodo (Android), and many others offer robust annotation features.

Mobile annotation is great for reviewing documents on the go. The touch interface works well for highlighting and quick notes, though detailed markup is easier on a larger screen.

Annotation Best Practices

Use Consistent Colors

Develop a color system and stick to it. Yellow for general highlights, green for approved sections, red for issues, blue for questions. This makes your annotations easier to understand at a glance.

Be Specific in Comments

"This section needs work" isn't helpful. "The tone here is too casual for a formal report — suggest revising to match section 3's style" is much better. The person reading your annotations should understand exactly what you're asking for.

Don't Over-Annotate

A page covered in highlights and comments is overwhelming. Be selective. If everything is marked up, nothing stands out. Focus on the most important issues.

Reply to Comments

If someone annotates your document and asks a question, reply directly to their comment. Most annotation tools support threaded discussions within comments. This keeps the conversation organized and attached to the relevant content.

Check Your Annotations in Different Viewers

Before sending an annotated PDF, open it in a different viewer to make sure everything displays correctly. Some tools create non-standard annotations that don't show up properly elsewhere.

Consider Flattening Before Final Distribution

Annotations are editable by default. If you're sending a final version and don't want recipients to modify your markup, flatten the PDF. This merges annotations into the document as static content — they become part of the image and can't be edited or removed.

Collaborative Annotation Workflows

When multiple people need to review the same document, annotations shine. Here's how to do it effectively:

Sequential Review

Person A annotates the PDF and passes it to Person B, who adds their comments, then passes it to Person C. Each person sees all previous annotations and can respond to them. At the end, you have one file with everyone's feedback.

Parallel Review

Send the original PDF to multiple reviewers simultaneously. Each person annotates their own copy. Then merge the annotated versions or manually consolidate the feedback. This is faster but requires more coordination.

Using Comment Status

Many annotation tools let you mark comments as "Accepted," "Rejected," "Completed," or "Cancelled." Use these statuses to track which feedback has been addressed. It creates a clear record of the review process.

Exporting and Sharing Annotations

Sometimes you need to share just the annotations, not the entire document. Most professional tools can export annotations as:

• A summary document listing all comments
• A CSV or XML file with annotation data
• An FDF (Forms Data Format) file that can be imported into another PDF

This is useful for creating reports of review feedback or importing annotations into document management systems.

Common Annotation Problems (and Fixes)

"My annotations disappeared"

This usually happens when you save the PDF without actually saving the annotations. Some viewers require you to "post" or "commit" annotations before they stick. Look for a save or commit button in your annotation toolbar.

"Annotations show up on the wrong pages"

If the PDF has been modified after you added annotations — pages inserted, deleted, or reordered — the annotations might end up on the wrong pages. Annotations are anchored to specific page numbers, not specific content.

"Recipients can't see my annotations"

Different PDF viewers handle annotations differently. If you're using advanced annotation features, test with the viewer your recipients use. You might need to flatten the PDF to make annotations visible everywhere.

"The file size got huge after annotating"

Some annotation tools, particularly those that save every pen stroke separately, create bloated files. If file size matters, compress the annotated PDF before sharing.

The Bottom Line

PDF annotation is one of those features that's been hiding in plain sight. Once you know it exists, you'll wonder how you ever worked without it. No more printing and scanning. No more trying to describe changes in email text. Just mark up the document directly, clearly, professionally.

The tools are everywhere — built into operating systems, available in browsers, installed on most computers already. You don't need expensive software or technical expertise. Just open a PDF and start marking it up.

My colleague who printed 40 pages and scanned them back in? He annotates PDFs digitally now. That hour-long process takes him five minutes. And his clients get clean, professional documents instead of crooked scanned pages.

Don't be the person printing documents in 2026. Annotate digitally. Your future self will thank you.