PdfDocument pdf = new PdfDocument();
pdf.LoadFromFile("result.pdf", FileFormat.PDF);
XmpMetadata meta = pdf.DocumentInformation.GetMetaData();
XmlDocument xmlfile = meta.XmlData;
xmlfile.Save("result.xml");
XmlDocument xmp=new XmlDocument();
xmp.Load("xmp.xml);
document.XmpMetaData.Load(xmp);