How to Password Protect a PDF (Free, No Upload)

Add a password to a PDF in 4 steps

1. 1

   Open Protect PDF and add your file

   Go to Protect PDF and drop the PDF onto the page, or click Choose file. Files up to 40 MB are accepted. Encryption runs in your browser with qpdf compiled to WebAssembly, so neither the file nor the password is sent anywhere.

2. 2

   Type the password twice

   Enter it in Open password, then again in Confirm password. The eye icon shows what you typed. A strength bar under the first box rates it from Weak to Strong; anything under 8 characters counts as weak.

3. 3

   Click Protect PDF

   The tool encrypts the file, then re-opens the result to confirm that your password opens it and that it does not open without one. That check appears under Checked by re-opening the new file.

4. 4

   Download the protected copy

   Click Download PDF. The new file keeps your original name with -protected added, so the unprotected original stays untouched on your device.

What kind of protection this adds

Protect PDF always uses AES-256, the strongest encryption the PDF standard defines. Page content, images, embedded files and the document metadata are all encrypted. Without the password, a reader sees nothing but an error or a password prompt.

Every encrypted PDF has two passwords. The open password (also called the user password) is the one you type and share. The owner password controls who may change the file's security. Unless you tick Set my own owner password, the tool generates a random 24-character owner password on your device, so the open password alone is not enough to rewrite the protection. Protect PDF sets no restrictions, so you never need that owner password and it is not shown.

Readers who open the file can print, copy and edit it as normal. If you also want to limit those actions, use Encrypt PDF or PDF Permissions instead.

How to choose a password that holds up

AES-256 itself is not the weak point. Someone who gets your file can try passwords offline as fast as their hardware allows, so the password is what decides how long it lasts.

• Use 12 characters or more. Four or five unrelated words make a long password that is still easy to type.
• Avoid names, dates and keyboard runs such as 1234 or qwerty; the strength meter caps those as weak.
• Send the password by a different channel from the file. If the PDF goes by email, share the password by phone or text message.
• Use a different password for each file you send to different people.

Password protect a PDF on a Mac with Preview

Preview can add an open password too. Open the PDF, choose File > Export, click Permissions, tick Require Password to Open Document, enter the password, and save. This is handy when you are offline and already in Preview. KissThePDF works the same way on Windows, Linux, Chromebooks and phones, and confirms the result by re-opening it.

Problems you might hit

• "This PDF is password-protected" when you add the file. The PDF is already encrypted. Remove the old protection with Remove PDF Password, then protect it again with the new password.
• The button stays disabled. Both boxes must match exactly. A red "Doesn't match yet." line appears under the confirm box until they do.
• You need to make it smaller too. Run Compress PDF first. Compression tools cannot read an encrypted file, so protecting should be the last step.

Frequently asked questions