public void SetDocument(XmlDocument document) {
byte[] outerXml = System.Text.Encoding.UTF8.GetBytes(document.OuterXml);
//Create PdfStream
PdfIndirectReference iref = stamper.Writer.
AddToBody(new PdfStream(outerXml)).IndirectReference;
stamper.Reader.AcroForm.Put(PdfName.XFA, iref);
}