How to Add Comments to PDF Free: Annotate and Review PDFs

Adding comments to a PDF is essential for reviewing documents, collaborating with teammates, or leaving notes for yourself. You do not need expensive software to do it. Here are the best free methods in 2026.

Method 1: Adobe Acrobat Reader (Free)

Adobe Reader is the gold standard for PDF annotation, and the comment features are completely free.

Open your PDF in Adobe Acrobat Reader
Click the Comment tool in the right panel (or press Ctrl + 6)
Choose from: Sticky Note, Highlight, Strikethrough, Underline, Text Box, or Drawing
Click where you want to add the comment and type your note
Save the PDF — comments are embedded in the file

Method 2: Browser-Based Annotation

Both Microsoft Edge and Google Chrome support PDF annotation without any extensions.

Microsoft Edge

Open the PDF in Edge
Click the Pen or Highlight icon in the toolbar
Draw, highlight, or add text directly on the PDF
Save the annotated version

Google Chrome

Chrome added basic PDF annotation in 2024. Open a PDF, click the pen icon in the toolbar, and you can highlight, add text notes, and draw on the document.

Method 3: Free Online PDF Annotators

If you do not want to install anything, use a browser-based tool:

Xodo PDF Studio Online: Full annotation suite — comments, highlights, drawing, stamps. Works in your browser with no signup required.
PDF24 Tools: German-based, GDPR compliant, free annotation tool. Files are deleted from servers after processing.
Sejda PDF: Clean interface for adding text, highlights, and shapes. Free for documents up to 200 pages or 50MB.

Method 4: macOS Preview

Mac users already have a powerful PDF annotator built in. Open any PDF in Preview and click the Markup Toolbar button (pencil icon). You get:

Text boxes and callouts
Highlight, strikethrough, and underline
Shapes, arrows, and drawing tools
Notes (appear as yellow sticky notes)

Types of PDF Comments

Sticky Notes: Clickable notes that expand on hover — great for longer feedback
Highlights: Mark important text with color — useful for study and review
Strikethrough: Show text that should be removed or changed
Insert Text: Indicate where new text should be added
Text Box: Place visible text anywhere on the page
Drawing: Freehand drawing, arrows, and shapes

Collaborating with Comments

Modern PDF annotation supports real-time collaboration. In Adobe Reader, you can share a PDF via email or cloud storage, and multiple people can add comments that appear in a unified comment panel. Each comment shows the author name and timestamp.

Privacy Tips for PDF Comments

Comments in PDFs can contain metadata including your name and the timestamp. Before sharing a final version:

Remove all comments and annotations
Use "Flatten" to permanently merge comments into the page content
Clean metadata using a PDF metadata cleaner

Frequently Asked Questions

Can I add comments to a signed PDF?

It depends on the certification level. Some signed PDFs lock all changes including comments. Others allow annotations without invalidating the signature.

Do comments increase file size?

Slightly. Text comments add minimal size. Drawing and image annotations add more. For most documents the increase is negligible (under 100KB).

Can people without Adobe Reader see my comments?

Yes. PDF comments follow the ISO PDF standard. They are visible in any PDF reader including browsers, macOS Preview, and third-party apps.