How can I install custom fonts on Android? I am trying to display a Powerpoint slide deck on an android tablet, but the slides contain fonts that don't exist in android.

Is there a way to install custom fonts on the tablet?  If so, how?
In general, no. Some apps will let you add extra fonts to your SD card and search for then there, but that's app-specific. 

If your device is rooted, you could replace the built in fonts with those of your choosing, but that's a system-wide change.