Add A Digital Signature to Generated PDF Document

Winnovative HTML to PDF Converter allows you to add digital signatures to the generated PDF document. In order to add digital signatures you need a certificate with private and public keys. These certificates are usually stored in a .pfx or a .p12 file in PKCS#12 format and they can be password protected. A digital signature is represented by a WinnovativeDigitalSignatureElement object which can be placed in any position in a PDF page. Below is a complete example of adding a digital signature to a PDF document.

Code Sample - Add A Digital Signature to Generated PDF Document

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Http;

using Microsoft.AspNetCore.Hosting;
using System.Drawing;

// Use Winnovative Namespace
using Winnovative;

namespace WnvHtmlToPdfDemo.Controllers.PDF_Creator.PDF_Security
{
    public class PDF_Creator_Digital_SignaturesController : Controller
    {
        private readonly Microsoft.AspNetCore.Hosting.IHostingEnvironment m_hostingEnvironment;
        public PDF_Creator_Digital_SignaturesController(IHostingEnvironment hostingEnvironment)
        {
            m_hostingEnvironment = hostingEnvironment;
        }

        [HttpPost]
        public ActionResult CreatePdf(IFormCollection collection)
        {
            // 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 = collection["htmlStringTextBox"];
                string baseUrl = collection["baseUrlTextBox"];

                // 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 = m_hostingEnvironment.ContentRootPath + "/wwwroot" + "/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 file to browser
                FileResult fileResult = new FileContentResult(outPdfBuffer, "application/pdf");
                fileResult.FileDownloadName = "Digital_Signatures.pdf";

                return fileResult;
            }
            finally
            {
                // Close the PDF document
                pdfDocument.Close();
            }
        }
    }
}

HTML Code with a Region Marked to Become a Digital Signature

XML

<!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>