Thank you for your post.
FileMaker Go can only save files to the current work area of the iOS device.
One option, after saving the PDF file to the iOS device, is to send the PDF file as an attachment in Mail to the email address of the host machine.
Hmmm, but couldn't you insert that PDF into a container defined to use External Storage to move a copy to the external storage folder on the server?
Excellent option! The PDF would indeed be stored in the external storage folder on the server.
And if you need that file in a different folder, once you have done that, it would be possible to set up a script that runs periodically in a client session of FileMaker Pro that exports newly added PDF's from that container field to a shared folder on the server.
It's a shame that Export Field Contents is listed as not compatible with server scripts since this is a script step that can be set up to work without any dialog boxes or other user interaction.Otherwise this could be a server scheduled script or even one performed on command from the iOS client using the new perform script on Server script step.