How to use Password protect PDF
- Choose the PDF.
- Enter the password needed to open it, twice.
- Optionally restrict printing, copying or editing, with a separate permissions password.
- Select Protect PDF and download the encrypted copy.
How the protection works
The PDF is encrypted with AES using 256-bit keys, the strongest method the PDF format defines, by qpdf, a widely used open-source PDF toolkit running in your browser. Without the password the file's contents are unreadable: every PDF reader, on every device, asks for the password before showing anything.
Encryption is only as strong as the password. A short or common password can be guessed by software trying millions of combinations offline, so use something long: a passphrase of four or more random words is easy to share by phone and very hard to guess.
Restricting printing, copying and editing
You can also set what people who open the file are allowed to do: print it, copy text from it, or edit it. Those permissions are protected by a second, separate password, so someone who can read the document can't simply lift them. Most PDF readers honour the restrictions, which deters casual copying and reprinting, but they're enforced by the reader software rather than by the encryption itself, so treat them as a deterrent, not a lock.
Keep the password safe
The file is encrypted on your device and the password never leaves it, which also means nobody, including us, can recover it if it's lost. Store it in a password manager, and send it to recipients by a different channel from the file, for example the PDF by email and the password by text message.
Common uses
Sending payslips, bank statements, medical records, contracts or tax documents by email, sharing a financial model with a prospective investor, or archiving personal documents in cloud storage. The encrypted copy is a new file; your original is unchanged.
What recipients see
When someone opens the protected PDF, their reader asks for the password before showing any page, whether it's Adobe Acrobat, Preview on a Mac, a browser, or a phone's files app. Nothing else about the document changes once it's open.
Questions
- How strong is the encryption?
- AES with 256-bit keys, the strongest method the PDF format supports, applied by qpdf. The protection is as strong as your password: use a long one, ideally a passphrase.
- Is my password sent anywhere?
- No. The PDF is encrypted in your browser and neither the file nor the password leaves your device. That also means nobody can recover a forgotten password, so keep it somewhere safe.
- Do the printing and copying restrictions really stop people?
- Most PDF readers honour them, which deters casual copying, but they're enforced by the reader, not by the encryption. The open password is the real protection.