Quick answer: Open your PDF, pick a tool such as Highlight or Note, drag or click on the page, then press Save PDF. Highlights, drawings and stamps are drawn onto the page; notes are saved as real PDF comments that appear in Acrobat and other readers.
Highlight, underline and strike through
Drag across text and the highlight snaps to the words, like a proper reader. Underline and strikethrough work the same way, useful for suggesting edits. A simple colour code helps reviewers: yellow for important, green for approved, red for problems.
Draw, boxes, circles, lines and arrows
The freehand pen works with a mouse, finger or stylus. Shape tools give cleaner results: a box round a paragraph, a circle round a figure, an arrow from a comment to what it refers to. Colour and thickness are adjustable and every shape can be moved after drawing.
Comment notes other readers can see
Click to pin a note and type your comment. Notes are saved as standard PDF comment annotations, not flattened, so the recipient sees a note icon and a list of comments in their reader. Existing comments are kept when you save.
Stamps
Drop a boxed stamp: APPROVED, REVIEWED, DRAFT, CONFIDENTIAL, PAID, REJECTED, FINAL or COPY. Handy for invoices, purchase orders and sign-off, and resizable like any other mark.
How to annotate a PDF
- Add your PDF. The Annotate toolbar opens.
- Mark up text with Highlight, Underline or Strikethrough.
- Add drawings, notes and stamps.
- Save PDF. Your original is not changed.
How the browser-based annotator works
The PDF renders with PDF.js, which also supplies the text positions highlights snap to, and markup is written with pdf-lib, both in your browser. Undo, redo and the Eraser cover every mark, and the original content is never altered. To change the text itself, use the PDF editor.
Privacy
Your PDF is opened and changed entirely in your browser, not uploaded or stored, with no account needed. Site analytics are covered in our privacy policy.
Frequently asked questions
Is the PDF annotator free?
Yes, with no signup, page limit or watermark.
Is my PDF uploaded?
No. The file is annotated inside your browser tab.
Will my notes show up in Adobe Acrobat?
Yes. Notes are standard PDF comment annotations, visible in Acrobat, Preview, Edge, Chrome and most readers.
Are highlights saved as comments?
No. Highlights, underlines, drawings and stamps are drawn onto the page so they look the same everywhere. Only notes are comments.
Are existing comments kept?
Yes. Comments already in the file are carried over when you save.
Can I remove an annotation?
Yes, before saving: use the Eraser, Delete or undo. Your original file stays unchanged.
Can I annotate on a tablet or phone?
Yes. Freehand drawing works with a finger or stylus.
Can I annotate a scanned PDF?
Yes for drawing, shapes, notes and stamps. Highlights will not snap to words on a scan, but you can drag a highlight box.
Other PDF tools
Accuracy note: Checked that notes open as comments in desktop and browser readers, and that earlier comments survive a save.
Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.