watermarking images

Question

Hello,

I want to develop one online application, which user enter any word (fname,lname) itself on images.
and also that image can be download his/her computers.

e.g
Like online form application.
user fill up online form it self and then his/her download that form.


But,I want fill up the form on image.

I have develop small application.
it's fill the form on one page and then click button then redirect all value to another page on images.
here it's working. but, when I try to export all details with image/pdf so, it's not working, meant it's not download images. 

code for export pdf file.

        Response.ContentType = "application/pdf";

        Response.AddHeader("content-disposition", "attachment;filename=TestPage.pdf");

        Response.Cache.SetCacheability(HttpCacheability.NoCache);

        StringWriter sw = new StringWriter();

        HtmlTextWriter hw = new HtmlTextWriter(sw);

        this.Page.RenderControl(hw);

        StringReader sr = new StringReader(sw.ToString());

        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 100f, 0f);

        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);

        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);

        pdfDoc.Open();

        htmlparser.Parse(sr);

        pdfDoc.Close();

        Response.Write(pdfDoc);

        Response.End();

Thanks,