Protect PDF
Protect your PDF files with strong encryption. This tool uses AES-GCM encryption with a password-derived key to secure your documents.
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How PDF password protection works
The PDF standard has built-in encryption. When you protect a document, the viewer does not simply hide it behind a prompt — the content streams, embedded images, and metadata are genuinely encrypted, and modern PDFs use AES with a key derived from your password. Without that password the bytes are unreadable, no matter which program opens them.
There are two distinct passwords in the specification. A user password is required to open the document at all. An owner password lets the file open freely but restricts actions such as printing, copying text, or editing. The first is real cryptographic protection; the second is a permission flag that well-behaved readers honour, and a determined tool can ignore. If your goal is genuine confidentiality, set an open password.
Why we built this tool
Anyone emailing a payslip, a signed agreement, an ID scan, or a client report eventually needs the file locked before it leaves their outbox.
Handing that exact file to a random web service in order to protect it defeats the purpose entirely — for the seconds it sits on their machine, it is unencrypted and out of your control. Because we run the encryption in your browser through WebAssembly, the plaintext version never leaves your device and neither does your password. Nothing about the operation touches our infrastructure, because there is no infrastructure to touch. One consequence follows directly from that: we cannot help you recover a lost password, so store it somewhere safe before you send the file on.
Tips and common mistakes
- A passphrase of four unrelated words is stronger and easier to remember than a short string of symbols and substitutions.
- Send the password separately from the document — emailing both together protects nothing at all.
- Owner passwords that only restrict printing or copying are advisory; use an open password when the content genuinely must stay private.
- Test the protected file by opening it yourself before you send it, and store the password somewhere you will still find it in a year.
Quick start: using Protect PDF
- Select the PDF you want to secure.
- Enter a strong password — length matters far more than symbol soup; a passphrase of several words is ideal.
- Choose any permission restrictions the tool offers, such as blocking printing or copying.
- Apply the protection and wait for the encrypted document to be built locally.
- Download it, then reopen the file to confirm the password prompt appears before you share it.
Send the password through a different channel from the file itself. To lift protection from a document you own, use Unlock PDF.