Well, if you're willing to spend money, there are some 3rd party libraries that may do what you want - else you dont have much other choice than to go the 'use interop' route which means Powerpoint must be installed on the machine you're running your desktop app on - you could then use interop to 'export' pages from the PowerPoint presentation in your choice of format
btw, the spec for the Powerpoint file
[MS-PPT]: PowerPoint (.ppt) Binary File Format[
^] 'yuck' - I havnt yet seen a free parser for it