object reference error while implement itextsharp

I assume, there may be some issue in the stream object. could you kindly check this link which may helps you to implement html to pdf

 https://stackoverflow.com/questions/25164257/how-to-convert-html-to-pdf-using-itextsharp

 protected void Unnamed1_Click(object sender, EventArgs e)
        {
            string HTMLContent = "

 public byte[] GetPDF(string pHTML)
        {
            byte[] bPDF;
            MemoryStream ms = new MemoryStream();
            TextReader txtReader = new StringReader(pHTML);

            // 1: create object of a itextsharp document class  
            Document doc = new Document(PageSize.A4, 25, 25, 25, 25);

            // 2: we create a itextsharp pdfwriter that listens to the document and directs a XML-stream to a file  
            PdfWriter PdfWriterr = PdfWriter.GetInstance(doc, ms);

            // 3: we create a worker parse the document  
            HTMLWorker htmlWorker = new HTMLWorker(doc);

            // 4: we open document and start the worker on the document  
            doc.Open();
            htmlWorker.StartDocument();

            // 5: parse the html into the document  
            htmlWorker.Parse(txtReader);

            // 6: close the document and the worker  
            htmlWorker.EndDocument();
            htmlWorker.Close();
            doc.Close();
            bPDF = ms.ToArray();
            return bPDF;
        }

System.NullReferenceException' in itextsharp.dll Object reference not set to an instance of an object.

but i have already add itextsharp.dll reference,still getting error

PdfWriter PdfWriterr = PdfWriter.GetInstance(doc, ms); in this line

Aravind Govindaraj

PdfWriter.GetInstance(doc, Response.OutputStream); // in lthis line getting error

may i know which line you are getting this error ?

I think saw an article in W3schools explaining that but I am not sure where.