protected void convertToPdfButton_Click(object sender, EventArgs e)
{
    // Create a PDF document
    Document pdfDocument = new Document();

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

    // Add a page to PDF document
    PdfPage pdfPage = pdfDocument.AddPage();

    try
    {
        string htmlWithDigitalSignatureMarker = htmlStringTextBox.Text;
        string baseUrl = baseUrlTextBox.Text;

        // Add a HTML string with a marker for digital signature to PDF document
        HtmlToPdfElement htmlToPdfElement = new HtmlToPdfElement(htmlWithDigitalSignatureMarker, baseUrl);
        pdfPage.AddElement(htmlToPdfElement);

        // Make the HTML element with 'digital_signature_element' mapping ID a link to digital signature properties
        HtmlElementMapping digitalSignatureMapping = htmlToPdfElement.HtmlElementsMappingOptions.HtmlElementsMappingResult.GetElementByMappingId("digital_signature_element");
        if (digitalSignatureMapping != null)
        {
            PdfPage digitalSignaturePage = digitalSignatureMapping.PdfRectangles[0].PdfPage;
            RectangleF digitalSignatureRectangle = digitalSignatureMapping.PdfRectangles[0].Rectangle;
                    
            string certificateFilePath = Server.MapPath(@"~/DemoAppFiles/Input/Certificates/wnvpdf.pfx");

            // Get the certificate from password protected PFX file
            DigitalCertificatesCollection certificates = DigitalCertificatesStore.GetCertificates(certificateFilePath, "wnvpdf");
            DigitalCertificate certificate = certificates[0];

            // Create the digital signature
            DigitalSignatureElement signature = new DigitalSignatureElement(digitalSignatureRectangle, certificate);
            signature.Reason = "Protect the document from unwanted changes";
            signature.ContactInfo = "The contact email is support@winnovative-software.com";
            signature.Location = "Development server";
            digitalSignaturePage.AddElement(signature);
        }

        // Save the PDF document in a memory buffer
        byte[] outPdfBuffer = pdfDocument.Save();

        // 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=Digital_Signatures.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
    {
        // Close the PDF document
        pdfDocument.Close();
    }
}