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Protect PDF with a Password Online

Encrypt PDF files with AES-256 directly in your browser. Your files and passwords are never uploaded.

🔒Local processing · No upload

Drop PDF files here or click to browse

Select one or more PDF files to encrypt with a password

Max 200 MB per file · Max 20 files · Max 500 MB total

Set open password

Please select at least one PDF file.

Your files and passwords are processed entirely in your browser. Nothing is uploaded to any server.

What is PDF Password Protection?

PDF password protection uses AES-256 encryption to secure your documents. When you set an open password, the PDF content is encrypted so that anyone who opens the file must enter the correct password. This is different from permission restrictions, which only limit actions like printing or copying but do not encrypt the content.

How to Protect a PDF with a Password

  1. Upload one or more PDF files by dragging them or clicking the upload area.
  2. Enter a strong password and confirm it by typing it again.
  3. Click "Protect PDF" to encrypt your files with AES-256.
  4. Download the encrypted PDF files individually or as a ZIP archive.

What is an Open Password?

An open password (also called a user password or document open password) is required to open and view the PDF. Without the correct password, the file cannot be read. This is the strongest form of PDF protection because the content itself is encrypted, not just access-restricted.

Why Process in Your Browser?

All encryption happens directly in your browser using the Web Crypto API. Your PDF files and passwords never leave your device. This is especially important for sensitive documents like contracts, financial records, and personal information.

Limitations

If you forget the password, the file cannot be recovered. Qudo does not store passwords or offer recovery services. Already-encrypted PDFs must be unlocked before re-encryption. Some older PDF readers may not support AES-256 encryption. Large files are limited by your device's available memory. This tool does not replace digital certificate signatures, permission management, or enterprise document management systems.

Data and Privacy

PDF files are processed entirely in your browser. Passwords are never stored, logged, or transmitted. Analytics events only record tool usage (start, success, failure) without any file names, passwords, or content. After processing, all temporary data is cleared from the page.

Frequently Asked Questions

Does Qudo upload my PDF?â–¼
No. All processing happens in your browser. Your files never leave your device.
Does Qudo save my password?â–¼
No. Passwords are used only during encryption and are immediately cleared. Qudo does not store, log, or transmit passwords.
What encryption method is used?â–¼
AES-256 (V=5, R=6), the PDF 2.0 standard for maximum security.
Can I recover a forgotten password?â–¼
No. Qudo does not save passwords and does not offer password recovery. You must keep your password safe.
Can I protect multiple PDFs at once?â–¼
Yes. You can encrypt up to 20 PDF files with the same password in a single batch.
Can I re-encrypt an already protected PDF?â–¼
You must first remove the existing password, then apply a new one. This tool does not bypass existing encryption.
Does it work on mobile browsers?â–¼
Yes. The tool works on any modern browser on desktop, tablet, or mobile.
Does encryption reduce PDF quality?â–¼
No. Standard PDF encryption does not re-render pages, so text, images, and vector content quality is preserved.
Why can't some older PDF readers open the file?â–¼
AES-256 requires PDF 2.0 support. Very old readers (pre-2008) may not support it. Modern readers like Adobe Acrobat, Chrome, and Edge all support AES-256.
What is the difference between password protection and a digital signature?â–¼
Password protection encrypts the file content to prevent unauthorized access. A digital signature verifies the identity of the signer and ensures the document has not been altered. They serve different purposes.

Related Tools

After processing, Qudo clears password fields and temporary file references. Browser memory management prevents web applications from guaranteeing physical memory erasure.