General section of a file's File Info, there is a checkbox for
Stationery Pad and
Locked option is pretty straightforward, but what does
Stationery Pad do?
Basically, it tells an app opening the file to open a copy.
You do this on files that you want to use like templates. Since the app is given a copy, you'll never accidentally change the original.
Basically, it automatically copies the file into its original location (as 'name copy') and lets you work on the copy.