The nice thing about disk images is that you can encrypt them and password protect them.
First make your file or files and pop them in a folder. Then go to Disk Utility (it’s in the Utilities folder in Applications) and then find ‘Files’ in the top line, and choose ‘new image/image from folder.’ Find the folder you want to use and give it a name or keep the one that comes up. Then choose an encryption level and make a password. That’s it. The file will be saved as a .dmg.
If you lose the password you will not be able to recover it from anywhere.