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Let’s say you have screenshots of sensitive information sitting on your desktop that you’d like to password protect. You know that images of tax, banking, wire transfer forms, etc. in the clear can easily be viewed by anyone with physical or remote access to your machine, but you’re unsure how to secure them. Unfortunately, macOS Preview doesn’t support file-level password protection, but there are quick workarounds that don’t require third-party software or downloading anything not already on your Mac.
Method 1: Overkill using DiskUtility
This first method might be a bit overkill if you’re looking to secure less than a handful of graphics files. It involves creating an encrypted virtual disk using DiskUtility. You can do this by gathering the screenshots (documents too even) and placing them in a folder. After this, head over to Finder > Applications > DiskUtility. In DiskUtility, go to File > New Image > Image from Folder and select the location of the folder you wish to encrypt.
From here, you can title the virtual disk (via DMG file), choose its location, level of encryption (up to AES-256 encryption), and image format. For the latter, I recommend choosing Read/Write. This will allow you to add or remove files later. Compressed, which is selected by default, compresses the contents to save space but is read-only. You’ve successfully created an encrypted DMG file containing all your private contents. The downside of this method is that you’ll have to mount and unmount the virtual disk each time…yuck.
Not to worry. There’s another solution that requires fewer clicks and can be done in seconds…
Method 2: Quick use of Preview
Enter Preview. Yes, the beloved built-in macOS image viewer we all know and love! By converting your graphics file to a PDF, you can unlock a handy password feature tucked away in its settings, turning your image into an encrypted password-protected PDF. This takes just a few seconds.
Below is a screenshot of some important tax info I’m using to estimate my quarterly taxes. But I don’t want it sitting duck on my desktop with its information in the clear. Even the preview icon gives away sensitive details.
Sure, you could try the old security-through-obscurity trick here and give the file a completely unrelated name like cook-recipes.png, but at the end of the day, it’s still unsecured. Why take the risk? After all, at the rate threat actors are adopting new AI techniques. It’s only a matter of time before they use it to sift through files regardless of their names.
1. Right-click and open with Preview
Right-click the image you want to password protect, hover over “Open With,” and choose Preview. Chances are, Preview’s already your default, so you can just double-click and it’ll pop open in Apple’s trusty image viewer. Ok, moving on…
2. Export the graphics file as a PDF
Next, go to File > Export as PDF.
Next, name your file, choose its location on your machine, and click More Details > Permissions to give us more options, including the one to add a password to the file.
3. Apply password to PDF file…done!
Check the “Require Password To Open Document” box and enter a password. This screen will also require you to enter an owner password even if you don’t plan to share the file, and no permissions are checked. You can enter the same password here.
Click on “Apply” and then click “Save,” and a new encrypted PDF will appear at your saved location.
That’s it! Now you can delete the unprotected file and empty your trash can.
Now, the next time you click on the newly created PDF to view its contents, you’ll be prompted to enter a password.
Unlike DiskUtility, which uses AES-256-bit encryption, Preview uses AES-128 when encrypting password-protected PDFs. This doesn’t necessarily mean your files are any less safe here. AES-128 produces a key size of 128 bits, still providing a huge number of possible key combinations, making any brute force attempts nearly impossible. Unless you’re harboring highly sought-after government secrets, it’s more than enough encryption against common threats.
Overall, this method might seem a bit long-winded at first, but once you’ve done it a few times, you can create these locked PDFs of sensitive images in seconds. Enjoy.
Security Bite is 9to5Mac’s weekly deep dive into the world of Apple security. Each week, Arin Waichulis unpacks new threats, privacy concerns, vulnerabilities, and more, shaping an ecosystem of over 2 billion devices.
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