How to password protect a PDF

Add a password

1. Open Protect PDF and add your file.
2. Type a password and enter it again to confirm. It needs at least 4 characters, but longer is much safer.
3. Choose whether people may print, copy or edit the document.
4. Press the button and download the protected file.

The encryption is AES-256 and happens on your device, so neither the PDF nor the password is sent to us.

Choose a password that holds up

• Aim for 12 or more characters, or a phrase of several unrelated words.
• Do not reuse a password from email or banking.
• Let the Password Generator create a random one and store it in a password manager.
• Share the password through a different channel from the file, for example by phone.

We cannot recover a forgotten password because we never see it, so keep an unprotected copy somewhere safe.

Opening or removing the password later

If you need to remove the password, Unlock PDF makes an unprotected copy once you enter the correct password.

Two kinds of PDF protection

There is a password to open the file, and there are permissions that say what people may do once it is open, such as print, copy text or edit. The open password is the real protection: without it the contents cannot be read. Permission settings are checked by the program showing the file, so a determined person can sometimes get around them. Use them to discourage casual copying, not to guard something secret.

Share the password safely

• Send the file and the password by different routes. For example, email the PDF and text the password.
• Do not put the password in the same email, or in the file name.
• Tell the person what the password is for, so a message with only a password does not look suspicious.
• For one-off sharing, use a password you will not use anywhere else.

What makes the password hard to guess

A protected PDF can be attacked by someone who has the file and simply tries many passwords on their own computer, so the length of your password matters more than any rule about symbols. A phrase of four or five unrelated words, or a random 14-character password from the Password Generator, is far stronger than a short word with a number added.

Before you send it

1. Open the protected file yourself and type the password, to confirm it works.
2. Keep an unprotected copy somewhere safe, since a lost password cannot be recovered.
3. Check that the file name does not give away private details, because the name is not encrypted.

AES-256 is supported by current PDF readers on computers and phones. Very old PDF software may not open it, so if the recipient has trouble, ask which program they use.

When a password is not enough

For the most sensitive documents, such as identity papers or medical records, avoid emailing them at all. Use a secure sharing link with an expiry date, or hand over the file in person. A password helps, but a document that never travels cannot be intercepted.

Frequently asked questions