Add A Digital Signature to Generated PDF Document

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, "winnovative");
            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();
    }
}

Protected Sub convertToPdfButton_Click(ByVal sender As Object, ByVal e As EventArgs)
    ' Create a PDF document
    Dim pdfDocument As 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
    Dim pdfPage As PdfPage = pdfDocument.AddPage()

    Try
        Dim htmlWithDigitalSignatureMarker As String = htmlStringTextBox.Text
        Dim baseUrl As String = baseUrlTextBox.Text

        ' Add a HTML string with a marker for digital signature to PDF document
        Dim htmlToPdfElement As New HtmlToPdfElement(htmlWithDigitalSignatureMarker, baseUrl)
        pdfPage.AddElement(htmlToPdfElement)

        ' Make the HTML element with 'digital_signature_element' mapping ID a link to digital signature properties
        Dim digitalSignatureMapping As HtmlElementMapping = htmlToPdfElement.HtmlElementsMappingOptions.HtmlElementsMappingResult.GetElementByMappingId("digital_signature_element")
        If digitalSignatureMapping IsNot Nothing Then
            Dim digitalSignaturePage As PdfPage = digitalSignatureMapping.PdfRectangles(0).PdfPage
            Dim digitalSignatureRectangle As RectangleF = digitalSignatureMapping.PdfRectangles(0).Rectangle

            Dim certificateFilePath As String = Server.MapPath("~/DemoAppFiles/Input/Certificates/wnvpdf.pfx")

            ' Get the certificate from password protected PFX file
            Dim certificates As DigitalCertificatesCollection = DigitalCertificatesStore.GetCertificates(certificateFilePath, "winnovative")
            Dim certificate As DigitalCertificate = certificates(0)

            ' Create the digital signature
            Dim signature As 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)
        End If

        ' Save the PDF document in a memory buffer
        Dim outPdfBuffer() As Byte = 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()
    End Try
End Sub

<!DOCTYPE html>
<html>
<head>
    <title>Add Digital Signatures in PDF</title>
</head>
<body style="font-family: 'Times New Roman'; font-size: 14px">
    <span style="font-size: 24px; font-weight: bold">Digital Signatures</span><br />
    <br />
    <span>The image and the text below will become a link to digital signature properties:</span>
    <br />
    <br />
    <div data-mapping-enabled="true" data-mapping-id="digital_signature_element" style="width: 320px; padding: 5px 5px 5px 5px; border: 2px solid royalblue">
        <span style="font-size: 16px; font-weight: bold; text-decoration: underline; color: navy">Click to open the digital signature properties</span><br />
        <br />
        <img alt="Logo Image" style="width: 300px" src="img/logo.jpg" />
    </div>
    <br />
    <br />
</body>
</html>