Encrypt your PDF document with a secure password to restrict access.
or click to browse local folders
Supports PDF/Image sizes up to 500MB
Executing operation locally in-browser...
Your processed document is ready for download.
Process Another FileEncrypt your PDF document with a secure password to restrict access. Process your documents 100% client-side in your web browser with zero file uploads, no signups, and no limits.
Run password protect pdf operations in real-time. Built with pdf-lib, document manipulation completes locally in browser memory sandbox within milliseconds.
Your confidential documents never touch external cloud servers. All processing happens 100% client-side on your local device for maximum data security.
No subscriptions, no hidden fees, no email registration, and zero watermarks stamped on your final PDF files.
The free online Password Protect PDF tool on PDFThunder.com lets you encrypt your pdf document with a secure password to restrict access. effortlessly. Whether you are working with corporate contracts, legal briefs, tax filings, or academic papers, our browser-based utility delivers professional-grade document formatting without needing expensive software installations like Adobe Acrobat Pro. Because PDFThunder compiles document streams locally using WebAssembly and JavaScript engines like pdf-lib, your files are never uploaded across the internet, protecting you from data leaks and network transfer delays.
Files are read and compiled using client-side memory buffers, making password protect pdf up to 10x faster than cloud converters.
Works on all web browsers (Chrome, Safari, Firefox, Edge) across Windows, macOS, Linux, iOS, Android, and Chromebooks.
Popular PDF web converters like iLovePDF, SmallPDF, and Sejda require uploading your sensitive files to cloud servers, which introduces privacy vulnerabilities and imposes strict daily file size limits unless you purchase a paid subscription. PDFThunder is built from the ground up as a 100% free, browser-native alternative. We impose zero file caps, require no user accounts, and never store or see your document contents. You can even load this page and use password protect pdf completely offline without an active internet connection!
Ctrl+D / Cmd+D) for 1-click access whenever you need to encrypt your pdf document with a secure password to restrict access..It implements standard PDF security encoding when packing files.