not 100% sure if your after a hidden subform to show up after a certain selection is made or if you want the user taken to a totally different form
e.g. click option 4 and get a new document opened in you face - im guessing the second option in whihc case I think you should be able to do this by using the app.openDoc("examplename.pdf") command
not one ive used myself but it should work much the same as the app.launchURL command which is usually quite stable
so you would have some code on your preferred event
to say something like
if (this.rawValue = "whatever value you want to trigger action";
app.openDoc("examplename.pdf")
alternatively if you other form is also online you could probably trigger it using the app.launchURL function - although the app.openDoc is meant to be the appropriate function for this type of thing
hope that helps - if not just clarify what your after and well try again!
cheers