iPhoto doesn't support pdf, only Jpeg. You can convert pdf to Jpeg with Preview or any number of apps - Graphic Converter, for instance.
There are many other slideshow apps, though I have no idea if they will support pdf. It's not really a standard format for images.
Alternatives to iPhoto's slideshow include:
iMovie, on every Mac sold.
Others, in order of price: PhotoPresenter $29
PhotoToMovie $49.95
PulpMotion $129
FotoMagico $29 (Home version) ($149 Pro version, which includes PhotoPresenter)
Final Cut Pro X $299
It's difficult to compare these apps. They have differences in capability - some are driven off templates. some aren't. Some have a wider variety of transitions. Others will have excellent audio controls. It's worth checking them out to see what meets your needs. However, there is no doubt that Final Cut Pro X is the most capable app of them all. You get what you pay for.