Protect PDF files
Add password protection to your PDF files.
What is Password Protect PDF?
Encrypt a PDF with a password using AES-256-GCM in your browser. Output is a protected .pdfx container that requires the password to reopen. Free and private.
When should you use it?
This tool is useful when you need to encrypt, unlock, sign, compare, or cover sensitive areas of a PDF.
How Password Protect PDF handles your file
A 256-bit key is derived from your password with PBKDF2 (100,000 iterations, SHA-256) and the file is encrypted with AES-256-GCM — all inside your browser.
Your device's own CPU does the work, so there is no upload wait and no server-side copy of your document to retain.
Good to know before you convert
- The output is a .pdfx container, not a standard encrypted PDF. It must be reopened with the PdfPix Unlock PDF tool; ordinary PDF readers cannot open it.
- Because it is a container rather than standard PDF encryption, it does not set PDF permission flags such as 'no printing' or 'no copying'.
- If you lose the password, the file cannot be recovered. There is no back door.
How to use Password Protect PDF
Upload the PDF file you wish to secure.
Enter and confirm a strong password.
Click 'Protect PDF!' to derive the key, encrypt the file, and download the protected .pdfx document.
Why choose PdfPix for Password Protect PDF?
Private by design
The file is never uploaded. Everything happens inside your browser tab, so there is no remote copy of your document to leak, retain, or subpoena.
No File Size Limits
Because conversions run locally using your computer's CPU power, we don't impose any artificial file size caps, queue delays, or wait times.
100% Free Forever
Get full access to all features without subscriptions, credit card inputs, or registration walls. No branding watermarks added to your outputs.
Universal Compatibility
PdfPix runs smoothly inside any modern browser on macOS, Windows, Linux, iOS, or Android, without needing external applications or plugins.
How PdfPixCompares to iLovePDF & Smallpdf
Unlike traditional cloud PDF services that upload your confidential documents to remote servers, PdfPix processes your files 100% in your browser. No file size paywalls, no task queues, and zero remote data retention.
Frequently Asked Questions
What level of encryption is used?
The file is encrypted with AES-256-GCM. The encryption key is derived from your password using PBKDF2 with 100,000 iterations and SHA-256, and a fresh random salt and nonce are generated for every file.
Does this lock editing and printing?
Not in the way a standard PDF permission does. PdfPix produces a .pdfx container that simply cannot be opened without the password, so there is no editing or printing to restrict. It does not set PDF permission flags for readers that open the file normally.
Can I open the .pdfx file in Adobe Reader?
No. A .pdfx file is a PdfPix container, not a PDF. To get a normal PDF back, upload it to the Unlock PDF tool and supply the password.
Will PdfPix store my password?
No. The key is derived and the file is encrypted locally in your browser. Your password is never transmitted and never stored.
Related PDF tools
Unlock PDF
Remove PDF password protection to unlock your PDF files.
Sign PDF
Add your signature to PDF documents easily.
Redact PDF
Permanently remove sensitive text and areas by flattening pages with the content destroyed.
Compare PDF
Compare two PDFs for structural differences in page count, dimensions, and rotation.
Related guides from the PdfPix blog
Step-by-step articles that show how to get the most out of Password Protect PDF in real workflows.