How to Annotate a PDF
Add comments, highlights, and sticky notes to any PDF online for free. No Adobe Acrobat needed.
About How To Annotate A PDF
Annotating a PDF adds visual marks — highlights, comments, shapes, and drawings — directly on the document without altering the underlying text. PDF AI Tools provides a complete annotation suite in the browser with no installation needed.
Go beyond basic highlighting: add sticky notes, draw shapes and arrows, use a freehand pencil tool, and insert stamps. All annotations are standard PDF format, readable in Adobe Reader and every major viewer.
How We Compare
Compared to desktop alternatives like Adobe Acrobat Pro (starting at $19.99/month), Smallpdf ($12/month for unlimited), or iLovePDF ($9/month Premium), PDF AI Tools delivers comparable quality at $0 for the core feature set. We skip the subscription friction by processing most operations directly in your browser with WebAssembly — no server infrastructure costs to pass on to users. Our AI features (summarization, chat, OCR) use a pay-as-you-go backend that keeps your total cost well under $5/month even for power users.
How to Use How to Annotate a PDF
- Step 1: Open your PDF in the Edit PDF tool
- Step 2: Choose an annotation type from the toolbar
- Step 3: Click or drag to place the annotation on the page
- Step 4: Download the annotated file when complete
Why Choose PDF AI Tools
We've built PDF AI Tools to replace expensive desktop software like Adobe Acrobat for 95% of common document workflows — at zero cost to you. Unlike competitors who gate features behind paywalls, add watermarks, or limit file sizes, our tools are genuinely free and genuinely unlimited. Your privacy matters: files processed client-side in your browser never touch our servers, and even AI-powered features use encrypted, auto-deleting processing pipelines.
Key Features
- Highlight, underline, and strikethrough text
- Sticky notes with colored flags
- Shape tools: rectangle, ellipse, line, arrow
- Freehand pencil tool
- Text box insertion
- Rubber stamp annotations (Approved, Draft, Confidential)
- Move, resize, and delete any annotation
- Annotations embedded in downloaded PDF
Frequently Asked Questions
Can I share my annotations with colleagues?
Yes — annotations are embedded in the PDF and visible to anyone who opens the file.
Are PDF AI Tools annotations compatible with Adobe?
Yes — we use standard PDF annotation types (PDF 1.4+) compatible with all major viewers.
Can I annotate a password-protected PDF?
Remove the password first using the Unlock PDF tool.
Can I delete an annotation after saving?
Annotations can be removed in any PDF editor after downloading.