If you use the config.pro option PLOT_NAMES YES, Pro/E will use .ps extension for postscript, .hp for HPGL, hp2 for HPGL2, .cal for Calcomp, .ver for Versatec & .ger for Gerber. PLOT_NAMES set to no makes all plotter output files with .plt extension. You can tell what type of file a .plt is by opening in a text editor if you are fluent in plotter languages.
I never use ProductView, but if it is anything like Pro/E you can configure it to produce output for all these types as well as tiff, CGM, etc. There are viewers avaiable for all these file types. I still prefer to generate postscript and distill it to PDF. It gives the best looking hardcopy, is robust and error free and everyone can view it without another viewer. Creating PDF's straight from WF3 has a lot of bugs at the moment.