Add Watermark to PDF Online — Free Tool
Add custom watermarks to PDF pages. Protect your documents with visible text overlays — all processing happens locally in your browser.
Why Choose Our PDF Watermark Tool?
Complete Privacy
Your PDF never leaves your device. Cloud watermark tools upload documents to servers. LocalPDF applies watermarks locally using client-side rendering.
Customizable Appearance
Control watermark text, position, opacity, rotation, and size. Create subtle background marks or prominent overlays.
No Watermark on Watermarks
Ironic but true — some free tools add their own branding when you watermark PDFs. LocalPDF never adds our logo or URL to your files.
Instant Processing
No upload delays. Watermarks render in your browser at native speed, typically under 3 seconds even for multi-page documents.
Preserve Original Quality
Watermarks are added as overlay layers without re-encoding the entire PDF. Original page quality and structure remain intact.
Batch Watermarking
Apply the same watermark to multiple PDFs sequentially without re-uploading or reconfiguring settings.
Key Features
How It Works
100% Private Sandbox: Your files never leave your device. All processing happens locally in your browser's secure memory.
Frequently Asked Questions
Are my files uploaded to a server?
Never. All processing happens 100% locally in your browser. Your files stay on your device, ensuring total privacy and security.
Is there a limit on file size?
There are no artificial limits. The only constraint is your device's available memory. Most modern computers and phones can handle large PDF files without issues.
Does it work on mobile devices?
Yes! LocalPDF Sanctuary is fully responsive and works on iOS, Android, and tablets through any modern web browser.
Technical Architecture: How it Works
Zero-Knowledge Architecture
Our system is designed so that your data is never seen by anyone else. Processing happens in the browser's secure memory space.
WebAssembly Performance
We use high-performance WebAssembly modules to achieve desktop-grade PDF processing speeds directly in your web browser.