Protect / Unlock PDF

What it's for

Put a password on a PDF so that only people who have it can open it, choose what a reader is asked to allow (printing, copying, changing, commenting), or take a password off a PDF you can open. The work is done by qpdf, a widely used PDF program, running in your browser as WebAssembly, so the file stays on your computer.

For example, when you need to email a tax return as a PDF, protect it with a password and send the password by another route.

How to use it

Choose the PDF, or drop it on the box. The box under it shows what qpdf says about the file’s encryption (the first time, the PDF engine of about 2 MB is loaded, and then it’s kept for offline use).

Protect it with a password: type an Open password twice. The file is encrypted with AES-256. An Owner password is optional: it is the password that lets someone change the permissions; if you leave it empty, one is made up and thrown away, so the permissions can only be changed by removing the protection with the open password. Untick what a reader may not do. You can also set only an owner password and leave the open password empty, to restrict a file that anyone can open.

Unlock it (remove the password): type the open password (leave it empty for a file that only has an owner password and restrictions). The saved copy has no encryption.

After saving, the page opens the new file with qpdf again to check it is protected, or unlocked, as asked, and only then saves it as name-protected.pdf or name-unlocked.pdf. Show the passwords makes the fields plain text.

Example

Choose any PDF, leave Protect it with a password selected, type correct horse in both open password boxes, untick Print, and choose Protect and save. You get name-protected.pdf, and the message says it is encrypted with AES-256. Opening it in a PDF reader asks for correct horse, and the reader then offers printing only if it ignores the restriction.

Good to know

A forgotten password can’t be recovered by this tool or anyone else: keep the password, and keep the original file. A short or common password can be guessed, so use a long one. The restrictions (print, copy, change) are requests that PDF readers choose to honour; some ignore them, and anyone who can open the file can take the protection off, so they only deter casual use. Only the open password keeps people out. Unlock only files you are entitled to open: this doesn’t guess or crack passwords, and it can’t open a file without its open password. Passwords can be at most 127 bytes, and one you set can’t start with a hyphen (qpdf would read it as an option), and a password with accented or other non-ASCII letters may not work in every PDF reader. Files with a digital signature no longer verify after either change. A damaged file may not be read at all. Encrypted metadata, attachments and the like are kept as the file had them. The PDF engine is qpdf 12.3.2 (see Credits), and what it makes should be opened in a reader to check before you rely on it. Nothing is uploaded.