Password protecting a PDF on Mac is straightforward — Preview handles it natively with no extra software required. Here's how to do it, what the protection actually covers, and when you might need stronger security.
How to Password Protect a PDF Using Preview
Open the PDF in Preview. Go to File > Export as PDF. In the export dialog, click the Permissions button in the bottom-left corner. Check the box next to Require password to open document and enter your chosen password in both the Password and Verify fields. Click OK, then click Save.
From that point on, anyone who opens the file — on Mac, Windows, iPhone, or any other device — will be prompted for the password before the content is shown. The protection travels with the file regardless of where it's sent or stored.
Setting Permissions as Well as an Open Password
Preview's Permissions dialog also lets you control what recipients can do with the file after opening it. You can set a separate Owner Password that restricts printing, copying text, and editing. This is useful when you're sharing a document that others can read but shouldn't be able to modify or redistribute freely.
The open password and the owner password are independent — you can set either one or both. A document with only an owner password opens without a password prompt but has restricted functionality; a document with an open password requires the password just to view it.
Password Protecting a PDF on Mac Using an Online Tool
If you need to protect a PDF that's already been shared or you prefer a browser-based workflow, WukongPDF's PDF Security tool handles it without needing to open Preview. Upload the PDF, set an open password, and download the protected file. This works on any Mac regardless of macOS version and is particularly convenient when you're already working in a browser.
Choosing a Strong Password
PDF password encryption is only as strong as the password you choose. Simple passwords like dates, names, or common words can be recovered quickly with automated tools. For genuinely sensitive documents — financial records, contracts, personal data — use a password of at least 12 characters mixing letters, numbers, and symbols, or generate one with a password manager.
Note that 128-bit RC4 encryption (used by older PDF tools) is weaker than the 256-bit AES encryption used by Preview and modern PDF software. If you're protecting high-sensitivity documents, verify that your tool uses AES-256 — Preview on macOS Catalina and later does.
What to Do if You Forget the Password
If you forget the password to a PDF you own, a PDF Unlock tool can recover access to files protected with simple or older passwords. Tools like WukongPDF's unlock feature attempt to remove the password restriction so you can open the file again. This works on many common protection scenarios, though very strong passwords with modern AES-256 encryption are unlikely to be recoverable this way.
The safest habit is to store passwords for protected PDFs in a password manager alongside the files they protect — so you never need recovery tools in the first place.