PDF Password Protector

What a PDF password does

Protecting a PDF encrypts its contents so it cannot be opened without the password. This tool uses AES-256, the strongest standard encryption defined for the PDF format, and checks the result after encryption to confirm the file really is locked before you download it. You can also block printing, copying text or editing, which is useful when you want people to read a document but not reuse it.

It is the simplest way to protect documents that travel by email or messaging: a tax return, a payslip, a medical report, a signed contract or a scan of an ID. If the message is intercepted, or sent to the wrong person, the file is unreadable without the password.

Choose a password you can defend

Encryption is only as strong as the password. Short or predictable passwords can be guessed by software that tries millions of combinations a second, no matter how strong AES-256 is.

• Length beats complexity. A passphrase of four or five random words is easier to remember and much harder to guess than an eight-character mix of symbols.
• Do not use names, birthdays, phone numbers or the document title.
• Do not reuse a password from your email or bank.
• Generate one with the Password Generator and test it with the Password Strength Checker if you want a second opinion. The article on password length versus complexity explains why long passphrases win.

Send the password separately

Never send the password in the same message as the file. If both travel together, the protection is only a small obstacle. Use a different channel: email the PDF and text the password, or share it by phone. For repeated exchanges with the same person, agree a password in advance.

Record the password somewhere safe, such as a password manager. A forgotten open password cannot be recovered from a modern encrypted PDF. If you lose it, the document is effectively gone unless you kept an unprotected copy.

Permissions: print, copy and edit

The permission options limit what someone can do after opening the file. They are useful as a deterrent against casual copying, but they are not a security barrier in the way the open password is. Some software ignores permission flags, and anyone who can open a document can photograph the screen. Treat permissions as a courtesy and the open password as the real lock.

A common setup for sharing a report is to leave the open password off, allow printing, and block editing and copying, so the document stays intact. A common setup for sensitive files is the opposite: a strong open password and full permissions for the person who knows it.

Before and after you protect

Finish editing first. Merge, split, rotate, watermark and compress the document, then protect the finished version, because most tools cannot work on an encrypted file. If you need to change a protected file later, use Unlock PDF with the password. Adding a "Confidential" stamp with Add Watermark to PDF before locking is a good extra signal.

The whole process runs in your browser, so neither the document nor the password is uploaded. The original file is left untouched; the protected copy is a new download. The longer guide on how to password protect a PDF walks through the steps on different devices.

Limits to know about

Protected PDFs may not open in very old viewers that do not support AES-256, though every current browser, Adobe Reader and mobile PDF app does. Password protection does not hide the file name, its size or the fact that a file exists. If even that must stay private, put the PDF inside an encrypted archive or a secure sharing service.