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PDF passwords explained: open passwords, permissions and encryption

Published September 28, 2026 by the ModifyPDF team

Adding a password is the simplest way to keep a PDF private when you email it or store it in a shared folder. But PDF security has two separate parts that are often confused, and only one of them actually keeps people out.

The two kinds of PDF password

Open password (user password)

An open password encrypts the whole document. Without the password, the file can’t be opened or read at all, and its text can’t be extracted. This is the kind of protection you want for anything confidential: payslips, medical letters, tax records, contracts.

Permissions password (owner password)

A permissions password lets people open and read the document but asks PDF readers to restrict certain actions, such as printing, copying text or editing. These restrictions are useful as a clear signal of how a file should be used, but they rely on the reading software honoring them. They are not a way to hide content: anyone who can read the document can, one way or another, reproduce what they see.

How strong is PDF encryption?

Modern PDFs support AES-256 encryption, the same algorithm family used to protect online banking and messaging. ModifyPDF’s Protect PDF tool uses AES-256, which current PDF readers such as Adobe Acrobat, browser PDF viewers, macOS Preview and mobile readers all support.

With strong encryption, the weak point is almost always the password. Attackers don’t break AES; they guess passwords, trying common words, names, dates and leaked passwords at very high speed. A short or predictable password can be guessed. A long, unique one can’t, in any practical amount of time.

Choosing a good password

  • Length matters most. Aim for at least 12 characters. A passphrase of four or five unrelated words is long and easy to type.
  • Avoid personal details like names, birthdays and the recipient’s ID number, which are the first things anyone would try.
  • Don’t reuse a password you use for an account.
  • Send the password separately. If the file and the password travel in the same email, the protection adds little. Text it, say it on a call, or use a different channel.

Protect PDF shows a checklist of common strength rules (length, upper and lower case, numbers and special characters) as you type.

Step by step

  1. Open Protect PDF and choose your file. Encryption happens in your browser; the file and the password never leave your device.
  2. Enter a strong open password.
  3. Optionally restrict printing, copying and editing with a separate permissions password.
  4. Download the protected PDF and open it once to confirm the password works.

Don’t lose the password

There is no “forgot password” for an encrypted PDF. If you lose the open password to a strongly protected file, the content is effectively gone. Keep your original, unprotected file somewhere safe, or store the password in a password manager.

Removing a password you know

Sometimes you need to take protection off, for example to merge a protected statement with other documents or to stop typing the password every time. Unlock PDF removes the password and restrictions from a file you are allowed to open: enter the password once and download an unprotected copy. It does not guess or crack unknown passwords. If you don’t know the password, ask the document’s owner for an unprotected copy.