Lock PDF File

Password Protect & Encrypt PDFs Free Online

Sharing sensitive files such as tax declarations, bank records, NDA agreements, or personal health records across email and cloud drives requires robust cryptographic protection. Our Free In-Browser PDF Locker empowers you to apply standard password protection to any PDF document in seconds.

Client-Side AES Cryptographic Pipeline

Conventional web lockers require uploading unencrypted documents to third-party cloud servers where intermediary disk caching risks document exposure. Free Qube eliminates this vulnerability completely. Our encryption engine utilizes the WebAssembly and Web Crypto API standards directly in your browser. Using the pdf-encrypt library, your chosen password generates a cryptographic key, scrambles document streams using AES encryption, and exports the secured PDF immediately—zero bytes are transmitted over the web.

Step-by-Step Encryption Guide

1. Choose Document: Select your target PDF file from your device.
2. Enter a Strong Password: Create a unique passphrase containing a mix of upper and lower-case letters, numbers, and symbols.
3. Lock Document: Click Lock & Download PDF to initiate local client-side cryptographic transformation.
4. Save Encrypted File: The protected document is immediately downloaded to your system with restricted permissions.

Technical Specifications

• Cipher Standard: Advanced Encryption Standard (AES) standard PDF handler.
• Key Derivation: Client-side cryptographic hash derivation conforming to ISO 32000-1 PDF standards.
• Processing Architecture: 100% In-Browser. No document or password telemetry.
• Cross-Reader Compatibility: Fully compatible with Adobe Acrobat Reader, Apple Preview, Google Chrome, and mobile PDF viewers.

Frequently Asked Questions