I'm trying to import a pdf form that I'd like to modify, however, during my attempt, I receive the following message, "FormsCentral could not import the PDF document because it has already been distributed by FormsCentral." What does this mean and what pdf's can I import?
Did you design the PDF in FormsCentral to begin with? If so you want to open the original form in FormsCentral and not import the exported PDF.
If you have deleted this FormsCentral form then you are out of luck for now. Very soon we will let you import PDF exported from FormsCentral but even after we enable this you won't be able to modify the PDF in FormsCentral.
If you first imported a PDF in FormsCentral then exported the submission enabled PDF from FormsCentral then you want to re-import the original PDF. If you dont have that PDF anymore or overriden it with the PDF you exported from FormsCentral then you might be able to follow the steps in this post to enable the import : http://forums.adobe.com/thread/1074856. This will also be fixed very soon and won't have to do those steps but that is your only options for now.
Hope this helps