How to Password Protect a PDF on Mac Using Preview (and Better Alternatives)

Preview is installed on every Mac and available without any configuration. The process is simple and takes less than a minute for any PDF regardless of length. Preview's encryption is baked into the standard PDF export process and creates a file that is recognized by all PDF viewers on any platform — Windows, iOS, Android, and Linux. The password you set must be entered by anyone who wants to open the file.

1. 1Open your PDF in Preview by double-clicking it in Finder — Preview is the default PDF viewer on macOS.
2. 2Go to File in the menu bar, then select 'Export as PDF'. In the dialog that appears, click the 'Show Details' button and check the box labeled 'Encrypt' — then enter and verify your password.
3. 3Click Save to export the password-protected PDF. The original file remains unchanged, and the new encrypted file is saved to your chosen location.

Apple's Preview uses AES-128 encryption for PDF password protection. This is the same standard used by the US government for classified information below Top Secret level and is considered secure for the vast majority of use cases. In practical terms, AES-128 encryption with a strong password cannot be cracked with any known attack in a reasonable timeframe. For most users — protecting a contract, a personal document, an invoice, or a confidential report — Preview's AES-128 encryption is completely sufficient. For users who specifically need AES-256 encryption — typically mandated by certain enterprise security policies, legal compliance frameworks like HIPAA, or organization-wide security standards — a browser-based tool like LazyPDF applies the stronger standard. LazyPDF processes the file entirely in your browser on your Mac, applies AES-256 encryption, and requires no software installation. If your organization's security policy specifies AES-256 for PDF documents, use LazyPDF for compliance. For everyone else, Preview is a perfectly good free solution that requires no additional setup.

Beyond the open password that encrypts the file, Preview also lets you set an owner password that controls what recipients can do with the document after opening it. In the Export as PDF dialog in Preview, when you check the Encrypt checkbox, you will see additional options including a checkbox for 'Require password to print document'. If you want to add more detailed restrictions — such as preventing copying of text or blocking modifications — you can use the Preview print dialog. Go to File, then Print, then click the PDF dropdown in the lower left corner and select 'Save as PDF'. In that dialog you can set both an open password and a separate permissions password. The permissions password controls printing, copying, and editing rights independently from the ability to open the file. This is useful when you want recipients to read the document but not redistribute its contents. For maximum control over both encryption strength and permission settings on Mac, LazyPDF's protect tool offers both user password and owner password configuration with AES-256 encryption in a straightforward interface.

Several common errors can lead Mac users to think their PDF is protected when it is not. The most frequent mistake is using the 'Save' command instead of 'Export as PDF'. If you open a PDF in Preview and use File → Save or Command-S, Preview saves changes to the file without applying any new encryption. The encryption option only appears in the Export as PDF dialog. Another common error is protecting a file but then sharing the original unprotected version from a different location. When you export a protected PDF in Preview, the encrypted version is saved to the location you choose in the export dialog. The original file in its original location remains unchanged and unprotected. Always confirm you are sharing the correct file by checking its name and verifying that a PDF viewer prompts for a password when you attempt to open it. A third mistake is using a very short or simple password. Preview applies the password as you type it with no complexity requirements, so it is entirely possible to set '1234' as the password for an AES-128 encrypted document. Use a minimum of 12 characters including uppercase, lowercase, numbers, and symbols.

Preview handles one file at a time, which is fine for occasional use but inefficient for protecting many documents. If you need to protect ten, twenty, or more PDFs on your Mac, there are better approaches. Automator, which comes pre-installed on macOS, can be used to create a batch PDF encryption workflow. Open Automator, create a new workflow, add a 'Get Specified Finder Items' action followed by 'Encrypt PDF Documents', set your password, and run the workflow against a folder of PDFs. This approach applies the same password to all files in the batch. For more sophisticated batch workflows — different passwords per file, progress tracking, or integration with cloud storage — a command-line approach using qpdf (installable via Homebrew with brew install qpdf) gives you full control. The command qpdf --encrypt password owner-password 256 -- input.pdf output.pdf applies AES-256 encryption from the macOS Terminal. For users comfortable with the command line, this is the most powerful free option available on Mac. For everyone else, Preview handles individual files reliably and LazyPDF handles those where AES-256 is required.