XFA forms seem to be becoming increasingly popular. T-Mobile, for example, now provides their bills *only* as XFA-encoded PDFs. The fact that poppler doesn't support this format makes it impossible to use any of these PDFs in any open source reader.
I had put some information here (https://bugs.kde.org/show_bug.cgi?id=299816) if is could help to implement that functionality !
*** This bug has been marked as a duplicate of bug 18935 ***