Annotate PDF — Free Online Tool

Annotation is the markup layer that turns a PDF from a passive document into a working surface for review and feedback. Whether you are reviewing a contract, marking up a manuscript, doing peer-review on a research paper, or coordinating edits on a design brief, the ability to drop comments, highlights, and shapes directly on the page is essential. Our annotation tool supports four primitive types: highlights with full color customization for emphasizing passages of text, text notes that appear as pinpoint markers and expand into popup commentary when clicked, rectangles for boxing off regions of the page or callouts, and circles for ringing specific elements. Each annotation can be individually positioned, sized, recolored, and deleted. Multi-step undo means you can experiment without committing. The output is a fully spec-compliant PDF with annotations embedded as proper /Annot dictionary entries — they show up correctly in Adobe Acrobat, Preview, browsers, and every annotation-aware reader. This is structurally different from rasterizing your markup onto the page (which is what cheaper tools do); the proper annotation dictionary entries mean your colleagues can click them, reply to them, or remove them.