xfdf
What is a .xfdf file?
application/vnd.adobe.xfdf
XFDF (XML Forms Data Format) is the XML representation of PDF form data — the modern, human-readable successor to binary FDF. It records each field name and value as XML elements and references the source PDF, making it easy to generate, diff, and transform with standard XML tooling. It is widely used to pre-fill and extract data from AcroForm PDFs.
How to use a .xfdf file
Use an example XFDF to test XML-based PDF form-data import/export, pre-filling AcroForms from a server, and parsing form submissions with ordinary XML libraries.