Annotate PDF Online Free — Highlight, Notes, Redact | Synthixx Tools
Annotate PDF documents online for free. Add highlights, strikethrough, underline, text notes, and redaction marks. Perfect for reviewing contracts, studying, marking up documents, or redacting sensitive information. Color-coded annotations make it easy to organize your notes. No signup, no watermarks.
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Annotate PDF documents:
- Highlight important text
- Add strikethrough or underline
- Insert text notes
- Redact sensitive information
How to Use
- 1Upload your PDF document — drag and drop or click to select
- 2Choose your annotation type — highlight, strikethrough, underline, text note, or redact
- 3Select a color for your annotation — yellow, green, blue, red, pink, or orange
- 4Enter the page number where you want to add the annotation
- 5Click 'Add Annotation' — repeat for as many annotations as needed
- 6Download your annotated PDF when finished
Features
- 5 annotation types — highlight, strikethrough, underline, text notes, redaction
- 6 color options — yellow, green, blue, red, pink, orange
- Add unlimited annotations to any page
- Redact sensitive information permanently
- 100% free — no account, no watermarks, no limits
- Private — files never leave your browser
- Works on any device — phone, tablet, computer
FAQ
How do I highlight text in a PDF?
Upload your PDF, select 'Highlight' as the annotation type, choose your color, enter the page number, and click 'Add Annotation'. You can add multiple highlights to different pages.
Can I redact sensitive information in a PDF?
Yes! Select 'Redact' as the annotation type. This draws a black box over the content area, permanently hiding the information. Perfect for removing personal data, financial info, or confidential text.
Is my PDF safe when I annotate it?
Absolutely. Your PDF is processed entirely in your browser — it never gets uploaded to our servers. All annotations are applied locally, so your document stays completely private.
What's the difference between highlight and strikethrough?
Highlight adds a colored overlay behind text to emphasize it (like using a highlighter pen). Strikethrough draws a line through the text to indicate it should be deleted or is no longer relevant.
Can I add annotations to specific pages?
Yes, you can specify exactly which page number each annotation should be added to. This lets you annotate different parts of your document with different colors and types.