protected void convertToPdfButton_Click(object sender, EventArgs e)
{
    // Create a HTML to PDF converter object with default settings
    HtmlToPdfConverter htmlToPdfConverter = new HtmlToPdfConverter();

    // Set license key received after purchase to use the converter in licensed mode
    // Leave it not set to use the converter in demo mode
    htmlToPdfConverter.LicenseKey = "fvDh8eDx4fHg4P/h8eLg/+Dj/+jo6Og=";

    // Set an adddional delay in seconds to wait for JavaScript or AJAX calls after page load completed
    // Set this property to 0 if you don't need to wait for such asynchcronous operations to finish
    htmlToPdfConverter.ConversionDelay = 2;

    // Set a handler for BeforeRenderPdfPageEvent where to set the background image in each PDF page before main content is rendered
    htmlToPdfConverter.BeforeRenderPdfPageEvent += new BeforeRenderPdfPageDelegate(htmlToPdfConverter_BeforeRenderPdfPageEvent);

    try
    {
        // The buffer to receive the generated PDF document
        byte[] outPdfBuffer = null;

        if (convertUrlRadioButton.Checked)
        {
            string url = urlTextBox.Text;

            // Convert the HTML page given by an URL to a PDF document in a memory buffer
            outPdfBuffer = htmlToPdfConverter.ConvertUrl(url);
        }
        else
        {
            string htmlString = htmlStringTextBox.Text;
            string baseUrl = baseUrlTextBox.Text;

            // Convert a HTML string with a base URL to a PDF document in a memory buffer
            outPdfBuffer = htmlToPdfConverter.ConvertHtml(htmlString, baseUrl);
        }

        // Send the PDF as response to browser

        // Set response content type
        Response.AddHeader("Content-Type", "application/pdf");

        // Instruct the browser to open the PDF file as an attachment or inline
        Response.AddHeader("Content-Disposition", String.Format("attachment; filename=Add_Elements_in_Background.pdf; size={0}", outPdfBuffer.Length.ToString()));

        // Write the PDF document buffer to HTTP response
        Response.BinaryWrite(outPdfBuffer);

        // End the HTTP response and stop the current page processing
        Response.End();
    }
    finally
    {
        // Uninstall the handler
        htmlToPdfConverter.BeforeRenderPdfPageEvent -= new BeforeRenderPdfPageDelegate(htmlToPdfConverter_BeforeRenderPdfPageEvent);
    }
}

/// <summary>
/// The BeforeRenderPdfPageEvent event handler where a background image is set in each PDF page
/// before the main content is rendered
/// </summary>
/// <param name="eventParams">The event parameter containing the PDF page being rendered</param>
void htmlToPdfConverter_BeforeRenderPdfPageEvent(BeforeRenderPdfPageParams eventParams)
{
    if (!addBackgroundImageCheckBox.Checked)
        return;

    // Get the PDF page being rendered
    PdfPage pdfPage = eventParams.Page;

    // Get the PDF page drawable area width and height
    float pdfPageWidth = pdfPage.ClientRectangle.Width;
    float pdfPageHeight = pdfPage.ClientRectangle.Height;

    // The image to be added as background
    string backgroundImagePath = Server.MapPath("~/DemoAppFiles/Input/Images/background.jpg");

    // The image element to add in background
    ImageElement backgroundImageElement = new ImageElement(0, 0, pdfPageWidth, pdfPageHeight, backgroundImagePath);
    backgroundImageElement.KeepAspectRatio = true;
    backgroundImageElement.EnlargeEnabled = true;

    // Add the background image element to PDF page before the main content is rendered
    pdfPage.AddElement(backgroundImageElement);
}