In general, there are two ways:
- protect from editing/changing (without a revision at least)
- protect from opening (without password)
Now I've looked at some old LibreOffice questions and some Stackexchange questions and even found this nice Wikipedia article about the MS Office password protection.
However, all of them mostly just seem to tackle the encryption when saving, i.e. the password to open a document.
However, there is no general overview and especially no evaluation on the security of the "editing lock" passwords.
Thus, how secure are both of these?