If you need to email a sensitive document—such as a tax return, a signed contract, or a document containing your bank details—sending an unprotected PDF file over the internet is a major security risk. If the email is intercepted, or if you accidentally type the wrong email address, anyone can open and read your private information.
Many users assume they need to purchase an expensive Adobe Acrobat subscription or upload their document to a questionable third-party “free PDF” website to lock their files. However, if you own a Mac, you already have a powerful PDF encryption tool built right into the operating system. Here is how to password protect any PDF using the native macOS Preview app.
How to Encrypt a PDF File Using Preview
Preview is the default application that opens when you double-click an image or PDF on your Mac. It is surprisingly robust and includes military-grade encryption features.
- Locate the PDF file on your Mac and double-click it to open it in Preview. (If it opens in another application, right-click the file, select Open With, and choose Preview).
- In the menu bar at the very top of your screen, click on File.
- From the dropdown menu, select Export… (Do not select “Export as PDF”).
- A new dialogue box will appear asking where you want to save the new file. At the bottom of this box, look for a checkbox labelled Encrypt.
- Check the Encrypt box.
- Two new text fields will appear: Password and Verify. Type a strong password into both fields.
- Click the blue Save button.
macOS will generate a brand new, encrypted duplicate of your PDF file in the location you selected. Your original, unprotected file will remain untouched.
Testing the Password Protection
Before you email the document, it is crucial to verify that the encryption was successful.
- Navigate to where you saved the newly exported, encrypted PDF.
- Double-click the file to open it.
- Instead of the document contents, Preview (or any other PDF reader) will immediately display a blank screen with a prompt reading: “This document is password protected. Please enter the password.”
- Type the password you created and press Enter. If the document opens successfully, your encryption works perfectly.
You can now safely attach this encrypted file to your email. Be sure to communicate the password to the recipient using a different method, such as a text message or a phone call. Never include the password in the same email as the secure document.
Can I Remove the Password Later?
Yes. If you decide you no longer want the document to be protected, you can strip the encryption away—provided you still know the original password.
- Open the encrypted PDF in Preview.
- Enter the password to unlock the document.
- Click File in the top menu bar, then select Export…
- In the save dialogue box, simply uncheck the Encrypt box.
- Click Save to create a new, unprotected version of the file.
By utilising this built-in macOS feature, you can ensure your personal data remains private without relying on expensive software or uploading your sensitive documents to unfamiliar cloud servers.
