There is only one file type that uses the .XDP extension:
XML Data Package
XML file created in the XML Data Package format, a file format developed by Adobe Systems for packaging PDF data into XML files; contains the entire PDF document contents including form and template data; may also include character-encoded sections for binary content.
The XDP format allows a PDF file to be transformed to XML and back to a PDF without losing information. It also enables any XML program to read the PDF data.
XDP files are supported by Adobe Reader, Adobe Acrobat, Adobe LiveCycle, and other Adobe programs.
Updated: October 14, 2018