private 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();

    Cursor = Cursors.WaitCursor;

    string outPdfFile = @"DemoAppFiles\Output\PDF_Creator\Digital_Signatures.pdf";
    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 = @"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();

        // Write the memory buffer in a PDF file
        System.IO.File.WriteAllBytes(outPdfFile, outPdfBuffer);
    }
    catch (Exception ex)
    {
        // The PDF creation failed
        MessageBox.Show(String.Format("Create PDF Document Error. {0}", ex.Message));
        return;
    }
    finally
    {
        // Close the PDF document
        pdfDocument.Close();

        Cursor = Cursors.Arrow;
    }

    // Open the created PDF document in default PDF viewer
    try
    {
        System.Diagnostics.Process.Start(outPdfFile);
    }
    catch (Exception ex)
    {
        MessageBox.Show(String.Format("Cannot open created PDF file '{0}'. {1}", outPdfFile, ex.Message));
    }
}