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Invalid Date 5 min read by Chirag Singhal

Annotating PDFs is one of the most common document tasks, yet many people don’t realize the full range of markup tools available to them. Whether you’re reviewing a contract, grading student papers, collaborating on a design, or simply taking notes while reading, PDF annotations let you add comments, highlights, drawings, and stamps directly onto documents without altering the original content. This guide covers every annotation type and the best tools for each task.

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Annotation types available

Non-destructive

Original content unchanged

Universal

Supported by all PDF readers

Collaborative

Multi-user review support

What Are PDF Annotations?

PDF annotations are additions to a document that don’t modify the underlying content. They exist as separate layers on top of the PDF, which means:

The original text and images remain unchanged
Annotations can be shown, hidden, or deleted independently
Different reviewers can add annotations without conflicting
Annotations persist across different PDF readers
They can include metadata like author name, date, and color

Feature	Annotation Type	Best Used For
Highlight	Marking important text passages	Yellow, green, pink, and custom colors
Sticky Note	Adding detailed comments	Collapsible icon with expandable text
Text Comment	Inline feedback on specific areas	Visible text box on the page
Drawing/Freehand	Circles, arrows, and sketches	Custom markup and emphasis
Text Strikethrough	Marking text for deletion	Editorial and legal review
Underline	Emphasizing text passages	Lighter emphasis than highlight
Stamp	Approval workflows and status	APPROVED, DRAFT, CONFIDENTIAL
Attachment	Linking related files	Reference documents and data

Types of PDF Annotations

Highlights and Text Markup

Text markup tools are the most frequently used annotations:

Highlight: Draws a semi-transparent colored band over selected text. Multiple colors are available, allowing you to create color-coding systems (e.g., yellow for important, green for approved, red for issues).

Underline: Places a line beneath selected text. Less visually intrusive than highlighting, useful for subtle emphasis.

Strikethrough: Draws a line through selected text, indicating it should be removed. Essential for editorial review and legal redline comparisons.

Squiggly underline: A wavy underline that draws attention without obscuring text. Often used to flag spelling or grammar issues.

Sticky Notes and Comments

Sticky notes are the workhorses of PDF review:

Appear as small icons that expand to show comment text
Can be positioned anywhere on the page
Include author name and timestamp automatically
Support rich text formatting in some readers
Can be replied to for threaded discussions

Drawing and Freehand Markup

Drawing tools let you annotate visually:

Freehand pen for custom drawings and signatures
Lines and arrows pointing to specific elements
Rectangles and ovals for highlighting areas
Polygons for irregular area selection
Cloud shapes for revision markers (common in architectural review)

Text Boxes and Callouts

Text boxes add visible text directly on the page:

Text boxes — text in a rectangular area
Callouts — text boxes with an attached arrow/pointer
Typewriter tool — add text anywhere as if typing on the page

Stamps

Stamps are predefined or custom images placed on the document:

Built-in stamps: Approved, Revised, Draft, Confidential, Sign Here
Dynamic stamps: Include automatically populated date, time, and author
Custom stamps: Your company logo, signature image, or custom graphics

Open the PDF in your annotation tool

Use a PDF reader or editor that supports annotations. Adobe Acrobat Reader (free), Foxit Reader, and most browser PDF viewers support basic annotations. Professional tools offer more options.

Select the annotation tool

Choose the type of annotation you want to add from the toolbar. Most tools group annotations into categories: text markup, drawing, notes, and stamps.

Apply the annotation

For text markup, select the text with your cursor. For notes and stamps, click where you want to place them. For drawings, click and drag to create the shape or freehand line.

Add your content

For notes and text boxes, type your comment. For stamps, select or upload the stamp image. Adjust colors, opacity, and other properties as needed.

Save the annotated PDF

Save the document to preserve all annotations. Most tools save annotations within the PDF file itself, making them portable and viewable by anyone who opens the file.

Best Tools for PDF Annotation

Free Tools

Adobe Acrobat Reader The most widely used free PDF reader includes solid annotation features:

Highlight, underline, and strikethrough text
Add sticky notes and text comments
Draw freehand and shapes
Use built-in stamps
Fill and sign forms

Web Browser Viewers Chrome, Firefox, Edge, and Safari include built-in PDF viewers with basic annotation support:

Highlight text
Add basic drawings (varies by browser)
Fill form fields
Free and always available

Foxit Reader A free alternative to Adobe Reader with robust annotation tools:

All standard annotation types
Typewriter tool for adding text anywhere
Measure tools for technical documents
ConnectedPDF features for collaboration

Professional Tools

Adobe Acrobat Pro The industry standard for comprehensive PDF annotation:

Advanced annotation tools and custom stamps
Comment tracking and export
Review and approval workflows
Integration with Adobe Document Cloud

PDF Expert (Mac) A popular Mac-native PDF editor with excellent annotation features:

Smooth freehand drawing with Apple Pencil support
Beautiful highlight colors and styles
Integrated note-taking experience
Fast performance with large documents

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Choosing a Tool

For occasional annotation needs, free tools like Adobe Reader or your browser’s built-in viewer are sufficient. If you annotate PDFs daily or need advanced features like stamps, comment export, or collaborative review, invest in a professional tool.

Annotation for Specific Use Cases

Legal Document Review

Lawyers and legal professionals use annotations extensively:

Redline comparisons: Use strikethrough and underline to show changes between document versions
Privilege markers: Apply colored highlights to mark privileged, confidential, or responsive documents
Issue codes: Use comment text to tag documents with legal issue categories
Bates stamps: Apply sequential numbering across document sets
Approval stamps: Mark documents as approved, signed, or executed

Academic Review and Grading

Educators benefit from structured annotation workflows:

Color-coded feedback: Use different highlight colors for different types of feedback (spelling, grammar, content, style)
Rubric stamps: Create custom stamps for common feedback points
Margin comments: Add detailed explanations using sticky notes
Track student progress: Compare annotated drafts to measure improvement

Business Collaboration

Teams use annotations for document collaboration:

Review cycles: Multiple reviewers annotate the same document with different colors
Status stamps: Mark sections as approved, pending, or rejected
Drawing markups: Circle, arrow, and sketch corrections on design proofs
Comment threads: Reply to annotations for discussion and resolution

Annotate Your PDFs with Ease

Use our free PDF tools to merge, organize, and prepare your annotated documents for review, collaboration, and distribution.

Explore PDF Tools

Managing and Organizing Annotations

Comment Pane

Most PDF tools include a comment pane that lists all annotations:

Filter by author, type, color, or page
Sort by date, page number, or author
Reply to create threaded discussions
Mark comments as resolved or checked

Exporting Annotations

Export annotations for documentation or processing:

Export to a summary document listing all comments
Export to FDF (Forms Data Format) for data exchange
Print a comment summary with page references
Copy comment text to a spreadsheet for tracking

Collaborative Review Workflows

For team-based document review:

Distribute the document to all reviewers
Assign colors to each reviewer for identification
Set a review deadline and communicate expectations
Collect annotated copies from all reviewers
Merge annotations into a single master document
Review and resolve each comment systematically
Create a response document addressing each annotation

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Annotation Best Practice

When adding comments, be specific about what needs to change and why. Instead of “fix this,” write “Change ‘quarterly’ to ‘monthly’ — our reports are generated monthly per the contract terms.” Clear comments save time and prevent miscommunication.

Removing and Hiding Annotations

Hiding Annotations

Most PDF readers let you toggle annotation visibility:

Hide all annotations to see the clean document
Show only annotations from a specific author
Show only certain annotation types
Toggle individual annotations on/off

Removing Annotations

Annotations can be removed without affecting the document:

Delete individual annotations by selecting and pressing Delete
Remove all annotations from a specific author
Delete all annotations of a certain type
Strip all annotations to produce a clean final version

Flatten Annotations

Flattening merges annotations into the document content:

Annotations become permanent parts of the page
They can no longer be independently edited or removed
Useful for creating final versions of reviewed documents
Reduces file size by eliminating annotation metadata

FAQ

Frequently Asked Questions

Can I annotate PDFs on my phone or tablet?

Yes. Most mobile PDF apps support annotation, including Adobe Acrobat Reader, Apple Books (iOS), Xodo (Android), and PDF Expert (iOS). Touchscreens with styluses like Apple Pencil provide the most natural annotation experience.

Do annotations increase the PDF file size?

Annotations add a small amount to file size, typically negligible for text-based annotations. Extensive freehand drawings or embedded image stamps can increase size more significantly. Compress the PDF after extensive annotation if file size is a concern.

Will my annotations be visible to others?

Yes. Annotations saved within a PDF are visible to anyone who opens the file. If you want to share the document without annotations, either delete them or use your reader's 'hide annotations' feature before sharing a screenshot, or flatten the document without the annotations.

Can multiple people annotate the same PDF?

Yes. Each annotation includes author metadata, so you can identify who added each comment. For simultaneous collaboration, use cloud-based tools like Adobe Document Cloud or dedicated review platforms that merge annotations from multiple reviewers.

How do I create custom stamps?

In Adobe Acrobat Pro, go to Tools → Stamp → Custom Stamps → Create. You can use any image file (PNG with transparency works best) as a stamp. Other professional PDF tools offer similar custom stamp creation features.

Can I search within annotations?

Yes. Most PDF readers allow searching comment text in addition to document content. The comment pane often includes a search or filter function specifically for finding annotations by keyword, author, or date.

Conclusion

PDF annotations are a powerful tool for review, collaboration, and document markup. From simple highlights and sticky notes to sophisticated drawing tools and custom stamps, the annotation features available in modern PDF tools can streamline virtually any document review workflow.

Start with the basic annotation types that match your immediate needs, and explore advanced features as your workflow demands. The time invested in mastering PDF annotation tools pays off in clearer communication, faster reviews, and more productive collaboration.