ASP.Net using iTextSharp Create PDF Document error at HTMLWorker.ParseToList

I am trying to generate a PDF using HTML template.

i am having trouble in parsing the html generated. here is my code

 using (FileStream fs = new FileStream(System.Web.HttpContext.Current.Server.MapPath("~/Documents/EmailTemplates/test.pdf"), FileMode.Create))
        {
            PdfWriter.GetInstance(document, fs);
            using (StringReader stringReader = new StringReader(contents))
            {
                List<iTextSharp.text.IElement> parsedList = HTMLWorker.ParseToList(stringReader, null);
                document.Open();
                foreach (object item in parsedList)
                {
                    document.Add((IElement)item);
                }
                document.Close();
            }
        }

i get error at HTMLWorker.ParseToList(stringReader, null); shows null reference, but stringReader has content needed