How to Annotate a PDF Online for Free
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What Is PDF Annotation?
Annotations are notes and marks placed on top of a PDF without altering the underlying content. Common annotation types include: highlights (colour-coded text emphasis), sticky notes (pop-up comments), underlines and strikethroughs (for editorial review), freehand drawings (for pointing out specific areas), and text boxes (for adding typed notes anywhere on the page).
Annotating in a Browser
Modern browsers handle basic PDF annotation. In Chrome, open a PDF and right-click to highlight text (on supported pages). For more complete annotation, open the PDF in Adobe Acrobat Reader (free) or upload it to Adobe Acrobat online (free tier) — both offer highlight, comment, and underline tools.
Best Free Online Annotation Tools
- Adobe Acrobat online — Free tier with highlights, sticky notes, and drawing tools. Files are processed on Adobe's servers.
- PDF24 — Browser-based, free, includes basic annotation. Files uploaded to server.
- Xodo — Free web and mobile app with excellent annotation support and real-time collaboration.
Saving Annotations Properly
Annotations can be saved in two ways: as interactive layers (reviewers can see and reply to comments) or flattened into the page (no further editing possible). When sharing for final review, save as interactive. When archiving or printing, flatten annotations first to ensure they display consistently.
Can I Remove Annotations Someone Else Added?
Yes — open the annotated PDF in Acrobat Reader, right-click any annotation, and choose Delete. You can also select all annotations and delete them in bulk. If you want a clean copy without any annotations, use the flatten method described in our guide to flattening PDFs.