fdf
What is a .fdf file?
application/vnd.fdf
FDF (Forms Data Format) is Adobe's format for carrying the field values of a PDF form separately from the document itself. An FDF file lists each form field name and its value and can reference the PDF it belongs to, so form data can be exchanged, imported, and exported without resending the whole PDF. It is the classic companion to interactive AcroForm PDFs.
How to use a .fdf file
Use an example FDF to test importing and exporting PDF form data, populating an AcroForm from external values, and round-tripping between a PDF form and its data file.