Per the FM Go 12 Development Guide, page 13, The Export Field Contents script step does the following:
"By default, the files created by script steps appear in the Files on Device list and are saved in the Documents folder. "
It turns out this documents folder is only accessible by the iOS application that saved the file, in this case FM GO. According to iTunes documentation ( http://support.apple.com/kb/HT4094 )
Which leads to the question: How can FM GO open PDF files in its own documents directory on the iPad? Other applications can do this, such as Adobe Reader.
Of course, one solution is to specify "Open Automatically" in the export field contents script step, then the document opens immediately (which may not be desired) in the iOS default pdf viewer (which happens to really stink, btw.)