Like do you want it to be unreadable, or unmodified, or just not deleted?
I don’t necessariy care for any of those. They are ‘bonuses’ if you will. Though…:
Unreadable will be required for preventing recreating the file elsewhere.
Unmodifiable is not necessarily required. Maybe I would like to ‘append’ something to an existing file. But I’m fine either way. It should not be possible to delete some of the original data though.