A draft contract lands in your inbox. You've got twenty-three observations across forty pages, and a typed email listing them all would take an hour to write and longer to act on. Comments solve this. You leave each note exactly where it belongs in the document, send it back, and your counterpart works through the file in order. This guide walks through commenting on a PDF in Flint's Annotate PDF editor — the different comment types, how to keep a review readable, and what survives when the file gets forwarded on.
Why comment on a PDF instead of emailing your feedback?
Emailed feedback is a list of references without anchors. “Page 4, third paragraph, where it says ‘net 30’ — should be net 14” takes longer to write and longer to find than a comment dropped directly on the “net 30” in the document. Comments stick to the place they refer to. The reader sees them in context. Round-trips collapse.
- Faster turnarounds. The author works through comments in document order rather than reconciling your list against their pages.
- Fewer misunderstandings. No more “which paragraph did you mean?” threads.
- A paper trail. The marked-up file becomes a record of the review — useful for legal documents, contracts, and design proofs.
The kinds of comments you can leave
Sticky notes
The classic. A small pin you drop anywhere on the page that opens to reveal your note. Doesn't obscure the underlying text. Best for longer thoughts and feedback that needs a narrative — “I'd soften this paragraph; it reads as confrontational and the spirit of the agreement is the opposite.” Sticky notes are the workhorse of any review.
Inline text comments
Type text directly onto the page — a label, a one-liner, a question. Useful when the comment is the intervention: writing “needs source” next to a statistic, or “TBD” next to a placeholder. Visible without clicking, which is good for short notes and unprofessional for long ones.
Callouts: arrow plus note
Pair an arrow with a sticky note. The arrow points exactly where you mean; the note says what to do. The clearest possible feedback for visual material — circle the element, arrow it, comment beside it. Perfect for design proofs and marketing assets.
Boxes and circles for “look here”
Rectangle or ellipse drawn around the region under discussion, often with a sticky note alongside. Useful when the comment refers to a chart, table, or image rather than a specific line of text. See the broader annotate a PDF guide for the rest of the shape toolkit.
How to add comments in Flint
Open the PDF in Flint
Pick a comment tool and place your note
Esc when you're done.Send the commented PDF back
About reply threads — let's be honest
Some PDF tools, notably Adobe Acrobat's commenting workflow inside their cloud product, support threaded replies where reviewers can respond to each other's comments in-document. Flint comments today are point-in-time notes: each one holds the text you wrote, but there's no built-in reply chain attached to it.
In practice this matters less than you'd think. Most review cycles work like this anyway: reviewer A marks up the document, hands it back, author updates and sends a v2, reviewer B marks up the v2. The PDF itself versions the conversation. If you genuinely need a comment thread on a single line, the cleanest move is a sticky note with each reviewer adding their initials and response on a new line:"CO: would soften this. JS: agree, suggest ‘may be subject to’."Ugly but functional.
If your review process leans heavily on threaded comments, worth knowing that limitation up front. For most reviews — contracts, drafts, design proofs — sequential PDF passes work better anyway.
What happens to comments when the PDF is forwarded
Comments are saved as standard PDF annotation objects, which means:
- They survive any reader. Acrobat, Preview, Chrome, Firefox, mobile readers, Kindle — every PDF viewer renders annotations correctly.
- They're editable by default. The person receiving the file can edit or delete your comments unless the PDF has been flattened.
- They show your name if you've added one. Some PDF tools attach an author name to each annotation; Flint records the comment but doesn't expose author metadata unless you add it manually to the note text. Useful to know if attribution matters for your review.
- Flattening makes them permanent. If you want comments locked in as part of the visual document, flatten the file via Edit PDF before sending. Useful when comments themselves are the deliverable — for example, when archiving a finished review.
After the review — sensible next steps
- Sign off. If the document is approved subject to your comments being addressed, drop a signature with Sign PDF. See the electronically sign a PDF guide if signatures are new to you.
- Compress before sending. Heavy comment loads can grow the file. Run Compress PDF if you're hitting email limits.
- Lock confidential reviews. Password Protect PDF encrypts the file so only the intended recipient sees the feedback.
- Combine the review pack. Multiple commented documents going to the same person? Merge PDF ties them into a single tidy file.
- Strip sensitive content. If your comments quote confidential material that shouldn't survive to the next reviewer, Redact PDF permanently removes it.
Other ways to comment (and where Flint fits)
Adobe Acrobat
The big one. Full commenting toolkit including threaded replies in the cloud product. Acrobat Reader (free) supports sticky notes and basic commenting; the cloud and Pro versions do more. Catch: monthly subscription, installation overhead, and the cloud commenting flow assumes everyone in your review has an Adobe account.
Preview on macOS
Free, built-in. Includes a respectable sticky-note tool. Mac-only and the commenting interface is dated. Fine for the occasional review on a Mac; not the right answer for cross-platform teams.
Google Drive's PDF preview
Upload to Drive, open in preview, click anywhere to add a comment. Threaded, with replies. Works well if everyone on the review has Google accounts and is comfortable with Drive. Less great if you want the comments embedded in the PDF itself rather than living in Google's metadata.
Flint
Any browser, any OS, no install. Comments embed as standard PDF annotations so anyone can read them anywhere. File stays in your Flint library across sessions. Honest about the threading limitation. Bookmark Annotate PDF if you're commenting regularly.
Tips for comments that actually get acted on
- Be specific. “Unclear” on its own forces a reply asking what's unclear. “Unclear whether this discount applies to renewals — please clarify” can be acted on immediately.
- One comment per issue. Don't stuff three separate concerns into one sticky note. They'll get partially addressed; the rest will be forgotten.
- Sort by severity, not by page. If you have critical and minor comments, label them — “BLOCKER:” prefix for must-fix items keeps the author's priority clear.
- Don't comment everything. If 60 percent of the document gets a sticky note, the signal drowns in the noise. Pick what matters.
- Initial your comments in multi-reviewer cycles. Since comment metadata isn't always exposed downstream, prefixing each note with your initials makes attribution obvious even after the PDF has moved through several hands.
Adding comments to PDFs: frequently asked questions
Will my recipient see the comments?
Yes. Comments are standard PDF annotations and render in any PDF reader — Acrobat, Preview, browser viewers, mobile apps, Kindle. No special software required on their end.
Can they reply to my comments?
Flint comments are point-in-time notes — there's no built-in reply thread. In practice, the common workaround is to add a second line to the original sticky note with the replier's initials, or to send a new version of the PDF with their own annotations on top.
Can I delete a comment I've added?
Yes — click the comment in the editor and delete it. Bulk deletion is available from the layer panel.
Are my comments private until I send the file?
Yes. Comments live in your private Flint library until you download or share. We don't train on or share your documents. Delete anything anytime from My Documents.
Can I make comments permanent so they can't be edited?
Flatten the PDF via Edit PDF before sending — this bakes the comments into the page layer so they're visible but no longer editable annotations.
Max file size?
250 MB on Pro.
Ready to leave some feedback?
Drop the PDF into Annotate PDF and you'll have the commenting tools in front of you in seconds. Sticky notes, inline text, arrows with callouts — everything you need to mark up a draft properly. When you're done, the rest of the toolkit — sign, compress, merge, lock — is one click away.