string filepath = "C:/Documents and Settings/Administrator/Desktop/PDFsharp/PDFs/BL.pdf";
           
            PdfDocument doc1 = new PdfDocument("Bill Of Lading instructions");

            doc1 = PdfReader.Open(filepath, PdfDocumentOpenMode.Modify);

            PdfPage page1 = doc1.AddPage();
            PdfAcroForm acroForm = doc1.AcroForm;
            PdfAcroField.PdfAcroFieldCollection fields = acroForm.Fields;