Turn your folder into a .dmg file to protect sensitive files
To create a password-protected folder on your Mac, follow these steps to turn your folder into a disc image file (.dmg).
1. If you haven't done so already, create the folder you want to encrypt and add your sensitive files to it.
2. Open the Applications folder on your Mac.
3. Open the Utilities folder.
4. Open the Disk Utility app.
5. From the menu at the top of your screen, to the right of the Apple icon, choose File.
6. From the File menu, choose New Image.
7. From the New Image menu, choose Image from Folder.
8. From the folder window that opens, choose the file you want to add a password to and click Choose. You can rename the file once you choose it, if you want.
9. In the window that has popped up, there are menus for Encryption and Image Format. You'll need to change both from the default choices.
10. Click the menu next to Encryption and choose "128-bit AES encryption (recommended)." If you want a higher level of security, choose "256-bit AES encryption (more secure, but slower)."
11. Once you have chosen your encryption level, a window will pop up that asks you to set your password. Click the key icon to the right of the password to see how secure your password is. In this popup, you can also choose to have a password created for you.
12. Enter the password twice and click Choose to set your password. Make sure you remember or make a note of your password. Otherwise, you won't have access to your files either.
13. Click the menu next to Image Format and choose "read/write."
14. Click Save. It will take a few moments for the app to create a disk image of your folder. Click Done to exit.
15. Your original folder still lives on your Mac, unencrypted. Once you are sure you can access the disk image and the files in it, delete your original folder.
How to use a password protected folder
Your password-protected folder will appear in your Finder window as a .dmg file. Double click to open it. You will be prompted to enter your password when you open the file.
The disk image of your folder will appear under Locations on the left side of your Finder window, choose the folder and enter the password to access the folder.