Hi,

I was having exactly the same problem as I wanted to send presentations to customers without them being able to modify them. I have just found the following trick:

1) Open normally your presentation in PPT/PPTX fromat
2) Save it as a slideshow (PPS/PPSX)
3) Using for example Windows Explorer find your PPS/PPSX presentation in its directory
4) Select your presentation and right-click on it
5) In the menu that appears select "properties"
6) In "Properties" mark the PPS/PPSX presentation as "Read-Only".

Now, when you send your presentation by mail, send the PPS/PPSX )not the editable PPT/PPTX). If the recipient tries to access the presentation interrupting the slide show by using ESC, the presentation just shuts down.

Test it by sending the presentation to yourself

Hope that helps

Regards