If you'd like to distribute your powerpoint but don't want people to modify it, try Touchshow.
Touchshow (PC end converter) converts ppt/pptx file to secret wtppt format so as to protect your content from being re-edited in distribution. Visit http://en.whytouch.com/touchshow-android.html to download the converter.
Touchshow (Android end player) could play wtppt file just like powerpoint. It supports slide transition effects, animation effects, gifs, flash animations (very important as there are lots of flash resources but nearly none of Android app could support it now), hyperlinks, triggers, audios and videos. As converter will combine all resources used into one file, it is easy to demo and share.
During playback, it also provides markup tool for user. It is useful for people to showcase their products and ideas direct on mobile, especially when your device support projection.
Wtppt could even be published as an android app, which makes your work cooler. As powerpoint is powerful in interaction, it is great for designer to showcase a prototype.
More than that, Touchshow allows running and interacting with user script coded by flash As3, which gives more imagination for your work. Accessing web service or local database, or implementing any function you need, it could now be used to develop applications for digital signage.
BTW, if you're a teacher and have many powerpoint coursewares, after converting them to wtppt, you'll be able to sell them online with our web service. Go on our web for the detail.