Your colleague sends you the draft proposal at 4:47 on a Friday. It needs a once-over by Monday. You don't want to type a fresh email listing twelve scattered comments — you want to mark up the PDF itself, hand it back, and let them work through your notes inline. That's annotation. This guide is a tour of every annotation tool Flint offers, when to use which, and how to keep reviews from devolving into chaos. Open Annotate PDF to follow along.
Why annotate at all?
Email comments lose their referent. “On page seven, third paragraph, the bit about the discount” takes longer to explain than the actual edit. Annotations stick to the place they refer to. The reader sees your note in context. Edits get made faster. Misunderstandings drop.
Concretely, annotation is the right move when you want to:
- Flag a specific phrase or section for the author to revise.
- Mark up a design or proof with circles around elements that need attention.
- Highlight key clauses in a contract before forwarding it on.
- Add your own notes to a document you're studying — the digital equivalent of margin scrawl.
- Run a review cycle where multiple people comment on the same draft.
The Flint annotation toolkit, end to end
Highlights
Drag across text. The selection lights up in your chosen colour. The annotation anchors to the underlying text run, so if the PDF gets re-rendered, the highlight follows. Use for studying, marking key clauses, or flagging text you want someone to focus on. There's a dedicated walkthrough on how to highlight text in a PDF if that's your main use case.
Sticky notes and text comments
Drop a marker anywhere on the page; click it to open a small text panel. Best for narrative feedback — “reword this”, “consider a different example”, “is this still the latest figure?” Keeps long-form thoughts out of the page itself.
Rectangles and ellipses
Drag to draw. Useful for circling a figure in a design proof, boxing in a paragraph that needs a closer look, or marking an element you want moved. Outline-only by default — pick a fill if you need to obscure something visually.
Arrows and lines
Drag from one point to another. Arrows are the universal “look here” gesture. Pair them with a sticky note for a labelled arrow: “move this caption up” with an arrow pointing exactly where you want it.
Freehand ink
Draw with your mouse or stylus. Use sparingly — freehand scribbles look unprofessional in business documents. Where they shine: marking up a sketch, signing in handwriting, or annotating an image that doesn't have selectable text.
How to annotate a PDF in Flint
Open your PDF in the annotator
Pick the tool that matches the comment
Mark up, save, share
Running a clean review cycle
Annotation tools are easy. Review cycles are where teams melt down. A few habits that keep things sane.
- Pick a colour code and stick to it. Yellow highlights for things you're flagging for the author. Red for must-fix issues. Blue for personal notes. Once everyone on the team uses the same convention, scanning a marked-up document becomes a glance.
- Keep one tool per comment type. Don't mix freehand circles with rectangles and ellipses for the same purpose. Pick one and use it throughout.
- Write tight notes. Sticky notes are not the place for paragraphs. If you have a long comment, write it in a separate doc and reference it from the sticky.
- One reviewer per pass. Two people annotating the same document at the same time produces overlapping comments and confused authors. Sequential passes work better.
- Always include the cleaned-up version. When you send the doc back, also send a flat un-annotated copy for reference. Some recipients prefer to see the document without the markup overlay.
After you've marked it up
- Send it back. Download and email the annotated PDF. Annotations survive — every PDF reader on earth understands them.
- Sign it. If the document is a proof that needs sign-off, drop a signature with Sign PDF next to your approval annotation.
- Compress it. Annotated PDFs sometimes grow slightly. Run Compress PDF if the file is going somewhere with size limits.
- Merge the marked-up version with others. Combining several annotated documents into a single review packet with Merge PDF is a tidy way to hand off a multi-doc cycle.
- Lock the result. If your annotations contain confidential feedback, Password Protect PDF encrypts the file before you send.
Other ways to annotate (and where Flint wins)
Adobe Acrobat Reader
The classic. Strong annotation toolkit. Free reader includes highlight, sticky note, and basic shapes. Catch: requires the Reader installed, and the UI hasn't aged kindly. Fine if Acrobat is already open.
Preview on macOS
Built into every Mac. Excellent for one-off markup. Limited if you want consistent colours or shapes across multiple documents — it tends to forget your last settings.
iPad with Apple Pencil
Genuinely lovely for freehand markup. If you have an iPad and a stylus, this is the gold standard for handwritten-feeling annotation. Less useful for typed sticky notes or precise rectangles.
Flint
Works in any browser, on any device, without installing a thing. All annotation types in one toolbar. Files stay in your Flint library, so you can pick up where you left off from any machine. Bookmark Annotate PDF if you do reviews more than occasionally.
Annotation tips worth remembering
- Less is more. A document peppered with 80 annotations is harder to act on than one with 12 clear ones. Cluster small fixes into a single sticky note where possible.
- Don't use highlights to obscure. A full-opacity highlight over sensitive text is not redaction — the text is still selectable underneath. Use Redact PDF if you actually need to remove content.
- Bigger shapes for printed review. If the annotated doc will be printed, draw shapes a touch larger than feels natural on screen — print resolution makes thin lines disappear.
- Pair arrows with notes. An arrow alone says “something here.” An arrow with a one-line sticky note says “what to do here.” Always more useful.
Annotating PDFs: frequently asked questions
Will my annotations survive when I send the PDF?
Yes. They're stored as standard PDF annotation objects, which every major reader (Acrobat, Preview, Chrome, Firefox, iOS, Android) renders correctly.
Can someone edit my annotations after I send them?
Yes — they're editable annotations by default. If you want them locked, the safest move is to flatten the file via Edit PDF before sending, or convert annotation marks into permanent edits. Most review workflows don't need this — but it's worth knowing.
Can I delete an annotation I've added?
Yes — click any annotation in the editor and hit delete. Bulk deletion is available from the layer panel.
Does Flint support sticky-note replies / threads?
Sticky notes are point-in-time comments — they hold the text you wrote, but there's no native reply thread. If your review involves multiple back-and-forth replies, simpler to version the document and exchange iterations.
Are my annotations private?
Yes. Files and annotations live in your private Flint library. We don't train on or share your documents. Delete them anytime from My Documents.
Max file size?
250 MB on Pro.
Ready to mark something up?
Drop your PDF into Annotate PDF and you'll have the full annotation toolbar in front of you in seconds. Highlights, shapes, arrows, sticky notes, ink — all in one editor, all preserved in standard PDF format when you download.