Lock PDF

Encrypt your PDF with bank-grade AES-256 security.

4.9/5 - 3,120 votes

Drag & Drop PDF files here

or click to browse from your computer

Files encrypted & deleted after processing.

Secure AES-256 for max protection.

Free to use, 100% online.

How to Password Protect PDF?

Secure your confidential documents in seconds. Add a strong password that encrypts your file contents completely.

1

Upload Document

Drag & drop your PDF. Connection is encrypted with TLS 1.3 for maximum safety.

2

Set Password

Choose a strong password. You can also set a separate 'Owner Password' for permissions.

3

Download & Lock

Download your protected file instantly. It can now only be opened with your password.

Important: Don't Lose It!

Because we use strong encryption, if you lose your password, the file cannot be recovered. We do not keep a copy of your password.

Engineering Philosophy

Bank-Grade Security.
Unbreakable Encryption.

We treat your privacy as our top priority. Our tool uses **AES-256**, the Advanced Encryption Standard used by governments and banks worldwide.

Unlike basic password tools that just add a flag, we fundamentally rewrite the PDF structure, wrapping every byte of data in a cryptographic layer that is mathematically impossible to brute-force with current technology.

Processing happens in isolated, ephemeral containers that are destroyed immediately after your file is ready. Your data never rests on our servers.

Crafted by Ex-Cybersecurity Engineers

AES-256

The highest standard of encryption available publicly.

Zero Logs

We don't store your files or your passwords. Ever.

Instant Erase

Files destroyed upon job completion.

Why Encrypt PDF Files?

Sending sensitive data like bank statements, contracts, or personal ID documents via email is risky. If your email is compromised, your data is exposed.

PDF Lock solves this by wrapping your file in a layer of mathematics. Even if a hacker intercepts the file, they only see random noise without the correct password.

Regular PDF vs. Encrypted PDF

Feature
Regular PDF
Locked PDF
Readability
Open to everyone
Password only
Google Indexing
Yes
No (Private)
Editing
Easy
Restricted
Copying Text
Allowed
Blocked

User vs. Owner Passwords

Start PDF Lock supports two types of passwords:

  • User Password: The password needed just to open and view the file. This is what most people need.
  • Owner Password: A stronger password that controls permissions. Someone with the User Password might be able to read the file, but not print or edit it unless they also have the Owner Password.

Key Terminology

AES-256

Advanced Encryption Standard (256-bit). The same encryption used by the US government for top-secret information.

Encryption Key

The secret string of characters (derived from your password) used to scramble and unscramble data.

Permissions

Settings that control what a user can do with a PDF (Print, Copy text, Edit, etc.).

Brute Force

A hacking method of trying every possible password. AES-256 is resistant to this.

Tips for Strong Security

Use Long Pass Phrases

Length beats complexity. "Correct-Horse-Battery-Staple" is harder to crack than "Tr0ub4dor&3" and easier to remember.

Different Owner Password

If you want to allow someone to read but not print, give them the User Password but keep a different, stronger Owner Password for yourself.

Tool Specs
AlgorithmAES-256
Compatible WithAll Readers
Key Length256-bit
Max File Size100 MB
Privacy Encrypted

Private & Secure

Your documents are processed in secure, isolated containers and are permanently deleted immediately after processing.

Enterprise Grade

Trusted by Professionals

"Finally, a tool that actually encrypts files securely. I trust this for my contracts."

M
Michael R.
Legal Consultant

"Great for sending employee data safely. I love the separate admin password feature."

E
Emily S.
HR Manager

Common Questions

Is it safe to use this tool?
Yes. Your file is transferred via encrypted SSL, processed in an isolated environment, and deleted instantly. We never see your password.
What happens if I forget my password?
Unfortunately, there is no way to recover it. AES-256 encryption is designed to be unbreakable. Please save your password in a password manager.
Can I remove the password later?
Yes! If you have the password, you can use our 'Unlock PDF' tool to remove the protection anytime.
Does this work on Mac and Windows?
Yes, it works on any device with a browser. The resulting PDF is compatible with Adobe Reader, Preview, Chrome, and all standard viewers.

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