If you open a PDF and you see this:
Chances are high that the PDF Form is actually a proprietary XFA Form, and not an AcroForm based on open standards. Documents created with Adobe LiveCycle Designer will be in the XFA format. PSPDFKit and other 3rd party frameworks will only be able to display documents based on AcroForm.
XFA Forms (XML Forms Architecture) represents a significant change in direction for Adobe from the popular FDF and XFDF methodologies. XFA Forms have their roots in a former e-forms company called JetForm later renamed Accelio and acquired by Adobe in 2002. XFA concepts were first introduced in PDF 1.5 (Acrobat 6) and expanded in PDF 1.6, (Acrobat 7). Unlike Adobe’s earlier forms technology XFA Forms utilize XML throughout. While XML is the backbone for all types of structured documents, there are distinct drawbacks to be considered:
(excerpt from Talking PDF)
You can read more about this topic here.
Most features that are possible with XFA are also possible using AcroForms, so you should simply convert your existing forms. Sadly Adobe really wants people not breaking out of their ecosystem, so converting XFA to AcroForm is tricky.