Protecting you project plan from unauthorized access or change
In my last post, I mentioned that I will describe the plan protection. So... here it goes...
First of all, there are two ways to protect your project plan:
1) Protecting from unauthorized access
2) Marking the plan as "Read-only"
Both ways require that you enter a password before saving the project plan (Save as->Tools->General options).

You can also check the "Read-only recommended" checkbox (as show in the picture) if you would like that users get a read-only recommendation windows when they open the project plan.
L.