Best Free PDF Annotation Tool in 2026

Updated for 2026

Annotating means highlight, comment, draw, and sign — not changing the text. Here are nine tools ranked for markup.

Bottom line: For free, private, browser-based signing and simple marks, PDFzen works. For full highlight/comment suites, Xodo, Adobe, or Foxit. For classroom use, Kami.

Sign & mark up a PDF — free, in your browser

How we picked

We ranked annotation tools on supported markups (highlight, underline, comment, draw, stamp, signature), platform, and whether files upload. PDFzen focuses on signatures and simple marks privately; dedicated annotators go deeper.

The comparison

Tool	Free?	Uploads file?	Key markups	Best for
Xodo	Freemium	Mostly local	Highlight, comment, draw	Cross-device
Adobe Acrobat Reader	Yes	No (local)	Highlight, comment, sign	Standard
Foxit Reader	Yes	No (local)	Highlight, comment	Lightweight
PDFescape	Freemium	Yes	Form + comment	Web edits
Kami	Freemium	Yes (cloud)	Classroom tools	Education
Hypothesis	Yes	Yes (web)	Web annotations	Research/share
PDF Annotator	Trial	Local	Ink, stamp	Tablet/pen
PDFzen	Yes, no account	No (in-browser)	Sign, simple marks	Private sign
Okular	Yes	Local	Highlight, comment	Open-source

Tool-by-tool review

Xodo

Best for: Cross-device markup

Xodo annotates across web, Windows, Mac, and tablet with highlights, comments, and drawing, mostly local with cloud sync on free/premium tiers. The best all-rounder if you switch devices.

Adobe Acrobat Reader

Best for: Standard

Acrobat Reader annotates and signs locally for free with reliable highlight/comment tools. The default most collaborators expect.

Foxit Reader

Best for: Lightweight

Foxit offers full highlight and comment tools locally and stays light. A great Acrobat alternative for daily markup.

PDFescape

Best for: Web edits + comments

PDFescape comments and lightly edits in the browser on a free tier with uploads and limits. Useful for quick web-based markups.

Kami

Best for: Education

Kami is built for classrooms — highlight, comment, voice notes, and assignments in the cloud (free/premium, uploads). Ideal for teachers and students.

Hypothesis

Best for: Shared web annotations

Hypothesis layers public/private annotations on documents for research and discussion; web-based with uploads. Niche but powerful for shared review.

PDF Annotator

Best for: Pen/tablet

PDF Annotator is a local Windows app focused on ink, stamps, and freehand — excellent with a stylus, but paid/trial rather than free.

PDFzen

Best for: Private sign

PDFzen adds your signature and simple marks in the browser with no upload and no account — honest about its lane. It is not a full highlighter, but for signing and light marks privately, it is instant and free.

Okular

Best for: Open-source

Okular annotates locally with highlights and comments, free and open-source. The Linux-friendly choice that also runs on Windows/Mac.

How we tested

We highlighted a paragraph, added a comment, and signed a page in each. Adobe/Foxit/Xodo did all three locally and fast; PDFzen signed privately in-browser; Kami/Hypothesis shone for shared/classroom contexts. Capability matched the use case, not file size.

Honest note: For private signing, PDFzen; for deep markup, Xodo/Adobe/Foxit; for class, Kami.

Which one should you pick?

Private signing: PDFzen in-browser, no upload.
Full highlight + comment: Xodo, Adobe, or Foxit (local).
Classroom: Kami.
Shared research notes: Hypothesis.

Choose by your platform

If you are on…	Use
Private signing	PDFzen in-browser
Full markup	Xodo / Adobe / Foxit
Classroom	Kami
Shared research	Hypothesis

Free vs paid: when to upgrade

Free annotation covers highlights, comments, and signatures. Pay for advanced ink, enterprise admin, or LMS integration.

Common mistakes when picking

Uploading files to annotate when local tools exist.
Picking a viewer that cannot highlight when you need markup.
Overlooking PDFzen for quick private signing.

FAQ