Step-by-step for Adobe Acrobat, Mac Preview, Windows (free) and the command line — plus what a password can't protect and what to do instead.
Updated October 2026
To password protect a PDF you encrypt it with an open password: nobody can read the file without it. You can do this for free on a Mac with Preview, on Windows with Microsoft Word or LibreOffice, or with Adobe Acrobat Pro. Use AES-256 encryption, a long password, and send the password through a different channel than the file.
PDFs support two different passwords. Most people need the first one.
| Open password (user password) | Permissions password (owner password) | |
|---|---|---|
| What it does | Required to open and read the file; content is encrypted | Restricts printing, editing, copying text and extracting pages |
| File opens without it? | No | Yes |
| How strong | Strong with AES-256 and a long password | Weak: many free tools and some PDF readers ignore or remove the restrictions |
| Use it for | Confidential documents sent by email | Discouraging casual edits, not real security |
If you want to stop people from editing rather than reading, see how to lock a PDF from editing.
You need Acrobat Pro (or Acrobat Standard). The free Acrobat Reader cannot add passwords.
Preview is built into macOS, so you don't need extra software.
Windows has no built-in PDF password option, but two free routes work well.
Online "protect PDF" tools are quick, but you upload the unencrypted document to a third-party server first. For contracts, financials or personal data, check the provider's retention policy or use an offline method.
On any system with qpdf installed you can encrypt a file with AES-256 in one command:
qpdf --encrypt OPEN_PASSWORD OWNER_PASSWORD 256 -- input.pdf protected.pdf
A password protects the file in transit. Once the recipient has the file and the password, you lose control:
Instead of attaching the PDF, upload it to HelpRange and send a secure link. The document stays on the server and you decide what the recipient can do:
Read more: how to restrict access to a PDF and how to prevent printing and downloading of PDFs.
Yes. On a Mac use Preview (File → Edit Permissions or File → Export → Encrypt). On Windows save the document as PDF from Microsoft Word with "Encrypt the document with a password", or use LibreOffice (File → Export as PDF → Security). Adobe Acrobat Reader cannot add passwords; you need Acrobat Pro.
An open (user) password is required to view the PDF and encrypts its content. A permissions (owner) password only restricts printing, editing and copying; the file opens without it, and many free tools can remove these restrictions.
It protects the file in transit if you use AES-256 and send the password through a different channel. It cannot stop the recipient from forwarding the file and password, saving an unprotected copy, or reading it after the deal is over. For that you need a secure link with access you can revoke.
Not with a password-protected attachment: once the file and password are shared, anyone who has them can open it. If you share the PDF through a secure viewer link instead, you can revoke access, set an expiry date and block downloading at any time.