[Therion] Compiler Preview Pane

In the XTherion Compiler window there is a Preview pane (bottom right) that is looking for a path to Acrobat Reader or to a pdf file. How does this work and what should it preview? My efforts generally come up with nothing at all, and once I think I got an error from Acrobat complaining about a corrupt file. May or may not have been related to my efforts with XTherion. Bruce