Whatever HTML string you have you can now pass it to the following code to convert to PDF using iTextSharp
string body = sb.ToStirng()
StringReader sr = new StringReader(body);
Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 100f, 0f);
HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
MemoryStream ms = new MemoryStream();
PdfWriter.GetInstance(pdfDoc, ms);
pdfDoc.Open();
htmlparser.Parse(sr);
FileStream file = new FileStream(Server.MapPath("~/Files/") + "Test.PDF", FileMode.Create, System.IO.FileAccess.Write);
byte[] bytes = new byte[ms.Length];
ms.Read(bytes, 0, (int)ms.Length);
file.Write(bytes, 0, bytes.Length);
file.Close();
pdfDoc.Close();
ms.Close();