Annotating a PDF — highlighting text, adding sticky notes, drawing, or leaving comments — takes less than a minute on any device. This guide covers every annotation type and the best free tools for Mac, Windows, iPhone, and browser.
Frequently Asked Questions
How do I annotate a PDF for free?
Every major platform has a built-in free option: Preview on Mac, Microsoft Edge on Windows, and the Files app Markup tool on iPhone. For browser annotation on any device without installing anything, Smallpdf and Xodo are free. The [Scanjet app](https://scanjet.app) is free for iPhone and lets you scan a paper document and annotate the PDF in one workflow.
What is the difference between annotating and editing a PDF?
Annotation adds a non-destructive layer on top of the existing content — highlights, notes, drawings — without changing the original text or layout. Editing modifies the actual document structure or text, which requires a dedicated PDF editor like Adobe Acrobat Pro.
Can I annotate a PDF on iPhone without a third-party app?
Yes. Open any PDF in the Files app, tap the share icon, and select Markup. You get highlighters, pens, shapes, a text tool, and a signature option — all built in with no download required. Changes save automatically when you tap Done.
Do PDF annotations get saved automatically?
It depends on the tool. Preview on Mac auto-saves annotations to the file. Browser-based tools like Smallpdf do not auto-save — you must click Download before closing the tab. In Microsoft Edge, press Ctrl+S before closing.
Can I annotate a scanned PDF?
Yes, but highlights only attach to individual words if the PDF has a text layer from OCR. To highlight scanned text precisely, first [make the PDF searchable](/blog/make-pdf-searchable/) by running OCR, then open it in any annotation tool. The [Scanjet app](https://scanjet.app) adds OCR automatically during scanning, giving you an annotatable text layer from the start.