Annotation (PDF)
A note, highlight, shape, or comment added on top of a PDF without modifying the underlying content — used for review, markup, and collaboration.
An annotation is any piece of markup added to a PDF that sits on top of the document rather than being part of its original content. Annotations are the PDF equivalent of writing in the margins or attaching a sticky note to a printed page.
Types of annotations
- Text notes / sticky notes — a comment anchored to a spot on the page
- Highlights — colored overlays over selected text
- Underlines and strikeouts — editorial marks
- Shapes — rectangles, circles, arrows, free-form drawings
- Stamps — standard marks like "APPROVED" or "DRAFT"
- Text boxes — boxes of added text, different from form fields
Why annotations are non-destructive
A PDF annotation lives in a separate layer of the file. The original content remains untouched underneath — which is why you can easily delete annotations without affecting the document. This makes annotations perfect for review cycles: reviewers add their feedback, the author sees the feedback, and the annotations can be removed or merged into a clean version.
When to flatten annotations
If you want the annotations to be permanent — baked into the document so no one can remove them — flatten the PDF. This merges the annotation layer into the page content permanently. Flattening is the standard final step before archiving a document that includes signatures or comments you want to preserve.
Tools
- Edit PDF adds text annotations to a PDF
- Flatten PDF permanently bakes annotations and form fields into the page content