What Is…? Reference Guides

Plain-language explainers for PDF annotation file formats, terms, and standards.

What Is FDF? The Forms Data Format for PDF Explained

Learn what FDF (Forms Data Format) is, how it differs from XFDF and embedded PDF annotations, and how to open, view, and convert FDF files easily.

Learn what XFDF (XML Forms Data Format) is, how it differs from FDF and PDF annotations, and how to open, view, and convert XFDF files easily.