PDF encryption: what it means and what to choose

1 min read·25 July 2026

When you protect a PDF, the file is encrypted. But what type of encryption is used, how strong is it, and does it matter which you choose? A clear explanation for everyone who wants to secure a PDF.

Encryption in PDF

PDF security uses symmetric encryption: the password is used to generate a key that encrypts the content. There are three main versions: 40-bit RC4 (weak, PDF 1.1), 128-bit RC4 (moderate, PDF 1.4), and 128- or 256-bit AES (strong, PDF 1.6/1.7+).

AES-256 is the standard

For current security you should always choose AES-256. PDFrust uses AES-128 or higher for protected PDFs. For long-term archiving or the most robust protection, choose a tool that supports AES-256.

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Owner password vs user password

PDF has two password types. The user password locks opening the file. The owner password restricts permissions (printing, copying, editing) but the file is still viewable. PDFrust supports both.

Password strength matters

The encryption is only as strong as the password. AES-256 with "1234" is trivial to crack. Use at least 12 characters with numbers, uppercase, and symbols. Store the password safely in a password manager.