If you don't want anyone to accidentally delete or modify a presentation, you can make it read-only, which allows everyone to continue reading and copying the contents, but not to change the presentation in any way. Files can be locked by using the Finder, which makes them read-only.
When a presentation has been made read-only, only the owner or those with Write privileges can remove the designation. If someone attempts to make changes to a read-only presentation, the changes can be saved only by making a copy of the presentation and giving it a new name.
