Unfortunately, by default they can be accessed by any computer they are plugged into, so if your external hard drive stores important data you should be encrypted and password protect the drive.

If you have a confidential PDF you want to password protect, you have a few ways to do that on your Windows 11 PC. You can use a desktop app or a web-based tool to encrypt your PDF files.

To password protect a PDF in Adobe Acrobat Reader, you'll need the paid Pro version, which starts at $14.99 a month.