Convert HTML To pdf using itextsharp in asp.net

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ASP.NET

I am having a prblem in converting html to pdf

The code which i used for conversion is as follows

using iTextSharp.text;
using iTextSharp.text.html.simpleparser;
using iTextSharp.text.pdf;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.IO;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;


protected void ConvertToPDFNow()
{
  StringWriter sw = new StringWriter();
        HtmlTextWriter w = new HtmlTextWriter(sw);
        print.RenderControl(w);
        string htmWrite = sw.GetStringBuilder().ToString();

Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=FileName.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);

        htmWrite = Regex.Replace(htmWrite, "</?(a|A).*?>", "");
        htmWrite = htmWrite.Replace("\r\n", "");
        StringReader reader = new StringReader(htmWrite);

        Document doc = new Document(PageSize.A4);
        HTMLWorker parser = new HTMLWorker(doc);
        PdfWriter.GetInstance(doc, Response.OutputStream);
        doc.Open();
        try
        {
                       parser.Parse(reader);
        }
        catch (Exception ex)
        {                   }
        finally
        {
            doc.Close();
        }
}

I am passing an html text which has image, table, inline-styles, id.
While converting i am getting an error "Object referenced not set to an instance" at
parser.Parse(reader);
What to do?