About This Tool
This tool encrypts your PDF with a genuine password using QPDF, the same open-source encryption engine relied on by developers and IT teams — compiled to WebAssembly so it runs entirely inside your browser tab. Your file is never uploaded anywhere: the password is set, the encryption is applied, and the protected PDF is handed straight back to you, all on your own device. The first time you use this tool your browser downloads the small QPDF engine (a one-time, cached download); after that it works instantly, even offline.
Open Password vs. Owner Password
- Open password (user password): what most people mean by "password protect." Nobody can view the file without typing it in — this is the field above.
- Owner password (permissions password): optional and separate. The file opens without it, but it can restrict printing, copying, or editing in viewers that respect PDF permissions. Advisory only — not a strong security boundary on its own, so don't rely on it alone for sensitive content.
When to Use AES-128 vs AES-256
AES-256 is the modern default and what we recommend — it's supported by every current PDF reader (Adobe Acrobat, Preview, Chrome, Edge). Only choose AES-128 if you specifically know the recipient is on very old software (roughly pre-2015) that can't open 256-bit encrypted files.
Good to Know
- There is genuinely no back door: PDF password recovery for AES-256 is not practically feasible. Store the password somewhere safe (a password manager, or the same secure channel you'll use to share the file) before you close this tab.
- To send the password separately from the file — never in the same email — for anything sensitive like bank statements, contracts, or ID documents.
- Need to remove a password instead? Use Unlock PDF — same private, in-browser approach, in reverse.
- Protect documents after you're done editing — merging, watermarking, or numbering an encrypted file requires unlocking it first.