Extract FDF data from a PDF in Go

To extract data from PDF to FDF, then export FDF as XFDF

doc := NewPDFDoc(filename)

// Extract annotations to FDF.
// Optionally use e_both to extract both forms and annotations
docFields := inDoc.FDFExtract(PDFDocE_annots_only) // PDFDocE_forms_only

// Export annotations from FDF to XFDF.
docFields.SaveAsXFDF(output_xfdf_filename)

// Optionally write XFDF to a string
xfdfStr := docFields.SaveAsXFDF()

PDF Form Fill and Form Data Extraction
Full sample code which illustrates basic FDF merge/extract functionality and full support for FDF (Forms Data Format)