export html to pdf using itextsharp

string str = HTML.ToString(); // StringBuilder to string
        Document document = new Document(PageSize.A4, 20, 25, 35, 35);
        try
        {

            PdfWriter.GetInstance(document, new FileStream(Server.MapPath(".") + @"\Chap0101.pdf", FileMode.Create));
            document.Open();

            iTextSharp.text.Image pdfImage = iTextSharp.text.Image.GetInstance(Server.MapPath("~/images/logo.png"));
            pdfImage.ScaleToFit(100, 50);
            pdfImage.Alignment = iTextSharp.text.Image.UNDERLYING; pdfImage.SetAbsolutePosition(180, 760);
            document.Add(pdfImage);

            
            //HTMLWorker hw = new HTMLWorker(document);
            

            //here error occurs
            List<itextsharp.text.ielement> htmlarraylist = new List<ielement>(iTextSharp.text.html.simpleparser.HTMLWorker.ParseToList(new StringReader(str), null));</ielement></itextsharp.text.ielement>
            foreach (IElement element in htmlarraylist)
            {
                document.Add(element);
            }
                    
            document.Close();
            ShowPdf("Chap0101.pdf");
        }
        catch (Exception ex)
        {

        }