MacHider is a file encryption tool that helps you protect your files. There are a few ways in which the application allows you to protect your files and add them to the interface. The easiest one is to use the drop zone. This is an area on the app's graphical user interface to which you can simply drag files that you want to protect. By default, the app comes with three custom groups (Secret Pictures, Private Files, AutoHide Group). These are all sample groups that help you understand the app. The most interesting one is the AutoHide Group. This one will automatically unhide all files within it when MacHider is active and hide them back when you close the app. You can of course create new groups that fit your needs. Other than hiding your files from Finder and other apps, MacHider can also password-protect them.
In my testing, I dragged a few files into the interface into one of the sample groups and manually hid them using the ON-OFF toggle. After that, the files were no longer accessible from Finder. The trial version of this app allows you to hide 3 files before you have to purchase it.