How to Annotate a PDF for Free in 2026 — Highlight, Comment & Draw

Annotating PDFs — adding highlights, sticky notes, comments, drawings, stamps, and text — is one of the most common things people need to do with PDF documents. Whether you're reviewing a contract, marking up a research paper, giving feedback on a design, or studying from a textbook, annotations make your thoughts visible without altering the underlying document.

The catch is that full-featured annotation in Adobe Acrobat costs money. The good news: every major platform has a free way to annotate PDFs, and in many cases the built-in tools are all you need. This guide covers every method.

What Is PDF Annotation?

PDF annotation means adding content on top of a PDF page without changing the underlying document. Annotations are typically stored as a separate layer — you can show or hide them, and they can often be removed or edited later. This is fundamentally different from editing the actual text of the PDF, which requires a PDF editor.

Common uses for PDF annotation include reviewing contracts and legal documents, providing feedback on reports or academic papers, marking up design mockups and architectural drawings, studying textbooks by highlighting key passages, and collaborating on shared documents.

Types of PDF Annotations

• Highlight — color overlay on text, like a physical highlighter. The most common annotation type.
• Sticky note / comment — a pop-up note attached to a location in the document
• Underline / strikethrough — text markup indicating corrections or emphasis
• Freehand drawing / ink — draw directly on the page with a mouse or stylus
• Text box — add typed text at any position on the page
• Shapes — rectangles, circles, arrows to point to specific areas
• Stamps — pre-made labels like "Approved," "Draft," "Confidential"
• Signature — add your signature to a document

Annotate on Mac — Free Built-In Tools

Mac has the best free built-in PDF annotation tools of any platform. Preview supports all major annotation types natively, and for more power, the Markup toolbar adds shapes, text, and signing tools.

Using Preview (Recommended for Most Users)

1. Open your PDF in Preview (double-click the file)
2. Click View → Show Markup Toolbar (or the pencil tip icon in the toolbar)
3. The toolbar shows: text selection, rectangle, ellipse, line, arrow, text box, signature, and highlight tools
4. To highlight text: select the text, then click the highlight color button
5. To add a sticky note: click the note tool, then click where you want the note on the page
6. To add a text box: click the "A" text tool and click to place it
7. Save with ⌘S — annotations are saved inside the PDF file

Using Safari's PDF Viewer

Opening a PDF in Safari gives you access to a basic markup toolbar too — the same highlighting and note tools from Preview. Useful when you've opened a PDF from a link and don't want to save it first.

Annotate on Windows — Free Methods

Windows doesn't have annotation tools built into its default PDF viewer (Edge can view but has limited markup). Here are the best free options:

Microsoft Edge (Built-In, Limited)

Edge's PDF viewer includes basic annotation: highlight in three colors, notes, draw freehand, and erase. Good enough for simple markup. Open your PDF in Edge (right-click → Open with → Microsoft Edge), then look for the pen and highlight icons in the top toolbar.

Adobe Acrobat Reader (Free, Most Features)

Adobe's free Acrobat Reader includes a solid annotation toolset: highlight, underline, strikethrough, sticky notes, drawing tools, stamps, and text boxes. It's the most feature-rich free option on Windows. Download from adobe.com — it's entirely free, though Adobe will try to upsell you on Acrobat Pro.

Foxit PDF Reader (Free)

A lighter-weight alternative to Acrobat Reader with excellent annotation support. Highlight, comment, draw, stamp, and sign — all free. Many people prefer it to Acrobat for its faster startup and cleaner interface.

Annotate on iPhone and iPad

iPhones and iPads have excellent PDF annotation built into the Files app and the Books app, plus Apple Pencil support on iPad for natural handwriting.

Using Files App (iOS/iPadOS, Built-In)

1. Open the Files app and tap your PDF
2. Tap the pen tip icon in the top-right corner to open Markup
3. Use the toolbar to draw, highlight, add text, shapes, or a signature
4. Tap Done to save. The file is automatically saved with annotations.

Using Apple Books

If your PDF is in Apple Books, tap and hold text to get the highlight menu, or tap the AA icon for notes and bookmarks. Best for reading and studying, less good for general markup.

Using GoodNotes or Notability (Free Tiers)

For heavier annotation work — especially handwritten notes on iPad with Apple Pencil — GoodNotes and Notability both offer excellent annotation. Both have functional free tiers, though some advanced features require a subscription.

Annotate on Android

Android doesn't have as seamless a built-in PDF annotation experience as iOS, but there are excellent free options:

Best Free Online PDF Annotators

No install required — these work in any browser on any device:

Flattening Annotations (Making Them Permanent)

Standard annotations are stored as a separate, removable layer in the PDF. Anyone with a PDF editor can delete your highlights and comments. If you need annotations to be permanent — for archiving, printing, or sharing in a way that preserves the markup regardless of what viewer the recipient uses — you need to flatten the annotations.

Flattening merges the annotation layer into the page content itself, making it non-removable and universally visible. Methods to flatten:

• Mac Preview: Print the annotated PDF to PDF. Go to File → Print → PDF → Save as PDF. The resulting PDF has flattened annotations.
• Adobe Acrobat Reader: Print to PDF using the built-in PDF printer.
• Online: PDF24's "Flatten PDF" tool (pdf24.org) can flatten annotations for free.

Pro Annotation Tips

• Use color coding consistently. Assign a meaning to each highlight color — for example: yellow = important, green = agree, red = disagree, blue = questions. Consistent color coding makes reviewing annotations much faster.
• Write specific, actionable comments. "See page 3" is not a useful comment. "The figure on page 3 contradicts the data in Table 2 — please reconcile" is. The more specific your annotation, the more useful the feedback.
• Keep a summary note on page 1. For long documents with many annotations, add a text box on the first page summarizing your main points. This gives the reader immediate context before diving into detailed markup.
• Number your comments if order matters. Some reviewers prefix notes with [1], [2], [3] so the author can address them in a logical order rather than jumping around the document.
• Save a clean backup before annotating. Keep an unannotated copy of important documents. If annotations need to be removed later, a clean backup is invaluable.

Frequently Asked Questions