Extract FDF data from a PDF in UWP

PDFDoc doc = new PDFDoc(fileName);

// Extract annotations to FDF.
// Optionally use e_both to extract both forms and annotations
FDFDoc documentFields = doc.FDFExtract(PDFDocExtractFlag.e_annots_only); //PDFDocExtractFlag.e_forms_only

// Export annotations from FDF to XFDF.
await documentFields.SaveAsXFDFAsync(outputXfdfFileName);

// Optionally write XFDF to a string
String xfdfString = documentFields.SaveAsXFDFString();