Reviewing a PDF without leaving comments is like reading a draft and saying "looks good" — useless to the author. Comments turn a static document into a conversation. They tell the writer where to clarify, the lawyer which clause to renegotiate, and your future self what you were thinking when you flagged page 12.
Types of PDF comments
PDF supports several comment types, and reviewers mix them up constantly. Each has a purpose:
- Sticky notes: a small icon that opens a popup. Best for general comments not tied to specific text.
- Highlights with comments: highlight a passage, attach a note. Best for "this sentence is wrong" or "great point."
- Strikethrough or underline with comment: clearer for "remove this" or "rephrase this."
- Text boxes: free-floating comments overlaid on the page. Useful for design feedback ("move this logo left").
- Drawing tools (pencil, arrow, shape): visual feedback. Best for diagrams and design proofs.
- Replies: every modern reader supports threaded replies on a comment. Use them — they keep conversations attached to context.
Method 1: Browser-based commenting
A browser PDF reader with annotation tools is the right answer when you don't want to install anything or upload the file. Docento.app lets you highlight, sticky-note, and draw directly in the browser, then download a PDF that includes all the comments.
Tips for clean comments:
- Use highlights for "I want to discuss this exact phrase." Use sticky notes for "this whole page needs work."
- Set a recognisable colour for your comments if multiple reviewers will work on the file. Yellow for first-pass, red for blocking issues, blue for suggestions, green for praise.
- Avoid drawing freehand unless the document is image-heavy. Hand-drawn arrows look unprofessional in formal review.
Method 2: Native readers (Preview, Edge, Chrome)
Most operating systems and browsers can comment without an extra app:
- macOS Preview: highlight, strikethrough, sticky note, shape, and text. Good enough for casual review.
- Microsoft Edge: strong PDF support including highlighting and notes.
- Chrome: highlighting and notes, but more limited than Edge.
- Acrobat Reader: full feature set, free, but heavier than the alternatives.
These all save comments back into the same PDF — anyone who opens the file in any other PDF reader sees them.
Method 3: Tablet and stylus
For markup that mixes typed comments with handwritten margin notes, a tablet beats a desktop. iPads with Apple Pencil, Android tablets with stylus support, and reMarkable tablets all save annotated PDFs that you can email back. The only thing to watch is file size: handwritten notes can balloon the PDF unless the app stores them as vector strokes rather than rasterised images. Check the saved file before sending.
Comment etiquette that authors actually appreciate
The same comment, written two different ways, lands very differently:
- "This is wrong." vs "This contradicts the figure on p. 14." The second tells the author what to fix.
- "???" vs "Unclear — does this apply to all customers or only enterprise?" Specific questions get specific answers.
- "Move this." vs "Move this above section 2 so the reader has context first." Reasoning prevents back-and-forth.
A comment is a gift to a future reader (often yourself). The more context you put in, the more useful it is.
Resolving and responding
Once the author addresses a comment, reply rather than delete. The conversation history is valuable when someone questions the change later. Many readers support marking comments as resolved — use it instead of clearing them.
For longer review cycles, export comments as a summary (Acrobat: Comments → Summarise comments) and circulate as a checklist. This is especially useful when the document is long and reviewers are remote.
Privacy and comment leaks
Comments often contain things the document author shouldn't see — internal review notes, candid feedback, personal information. Two safety habits:
- Never send a PDF with internal review comments to an external party. Either accept all changes (where applicable), redact the comments, or flatten the document, which removes interactive annotations.
- Strip metadata before sending, since comment authors and timestamps are stored in the PDF. Our guide on stripping metadata covers this.
Comments don't survive print or flatten
A printed PDF doesn't include sticky notes — they live as interactive layers. If you need comments to appear on paper, configure the print dialog to include "Document and markups" or use Comments → Print summary. After flattening, comments become permanent ink on the page; this is irreversible, so flatten only when you mean it.
Conclusion
Use the right comment type for the feedback. Use a colour code for multiple reviewers. Reply rather than delete. And before sending the file outside your team, scrub anything you wouldn't want the recipient to read. Docento.app handles annotation in the browser without upload, and pairs well with our annotation guide when you want a fuller feature reference.