Do you need to share your presentations with others? If yes, it’s a good idea to make sure that your presentations are set to be read-only before you share them. What you need then is the Mark as Final option in PowerPoint, which makes your file read-only. Note that this option is not as restrictive as password protecting a PowerPoint presentation. The Mark as Final option tries to prevent users from typing, editing commands, and proofing. All editing options are disabled or turned off. However, do remember that Mark as Final is not a security feature and it can be easily reversed by the recipient of your file.
For more details, choose your version of PowerPoint: