Digitally signing a PDF document resulted after HTML to PDF conversion

Question

I'm using the HTML to PDF converter tool from Winnovative to convert a HTML to a PDF with a table of contents. I did this using the code below:

// Create a HTML to PDF converter object with default settings
HtmlToPdfConverter htmlToPdfConverter = new HtmlToPdfConverter();

// Enable the creation of a table of contents from H1 to H6 tags found in HTML
htmlToPdfConverter.TableOfContentsOptions.AutoTocItemsEnabled = autoTableOfContentsCheckBox.Checked;

// Convert the HTML page to a PDF document in a memory buffer
byte[] outPdfBuffer = htmlToPdfConverter.ConvertHtmlToPdf(myBookHtml, baseUrl);

This works very well but the requirement is to also sign the PDF document which will be distributed as part of our software using a digital certificate I can export from our IIS server. How can I do this?

Answer 1

First, from IIS you have to export a certificate containing both private and public keys in a password protected PFX file. The you can use to file to sign the created PDF document using the following code:

// Create a HTML to PDF converter object with default settings
HtmlToPdfConverter htmlToPdfConverter = new HtmlToPdfConverter();

htmlToPdfConverter.TableOfContentsOptions.AutoTocItemsEnabled = true;

Document pdfDocument = null;
try
{
    string htmlWithDigitalSignatureMarker = htmlStringTextBox.Text;
    string baseUrl = baseUrlTextBox.Text;

    // Convert a HTML string with a marker for digital signature to a PDF document object
    pdfDocument = htmlToPdfConverter.ConvertHtmlToPdfDocumentObject(htmlWithDigitalSignatureMarker, baseUrl);

    // Make the HTML element with 'digital_signature_element' mapping ID a link to digital signature properties
    HtmlElementMapping digitalSignatureMapping = htmlToPdfConverter.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();

}
finally
{
    // Close the PDF document
    if (pdfDocument != null)
        pdfDocument.Close();
}