Hi Tom
I think that if PowerPoint did the things you've specified easily there'd be no need for specialist quiz products like QuizMaker!
That said, most, if not all, of what you've described could probably be done in PowerPoint using VBA macro functions. For example, in broad terms you could:
1. Specify a global variable, e.g. TotScore
2. Increment TotScore by 1 whenever someone clicked specific buttons (i.e. the correct answers) on any slide in the presentation
3. If TotScore was greater than your desired passing score you could set another variable PassStatus to 'Passed' otherwise set PassStatus to 'Not Passed' and display that on a certificate slide.
This wouldn't be foolproof. Anyone who knew their way around PowerPoint could probably reverse-engineer the correct answers by poking around the backend of PowerPoint.
Anyhoo, just my two cents' worth based on what you asked. Someone else may have a better idea.
Good Luck!