how do i save powerpoint so nobody can edit the file?

Answer 1

Save it as a PowerPointShow (*.pps) format.

For some interesting info check this:

http://www.lifehacker.com/software/powerpoint/save-your-powerpoint-presentation-as-a-show-180057.php

Answer 2

apply readonly property
procedure:
1.save the file as usual
2. right click the mouse on the powerpoint file
3. apply the readonly property(i.e click the read only check box)

Answer 3

tools> options> security tab

enter a password to modify. Don't forget this one though, because it is hard to recover the password if you forget it.