Adding a digital and visible signature to a PDF

SigningPdf.cs

using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.security;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;
using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace SignedReport
{
    class SigningPdf : IDisposable
    {
        PdfReader reader = new PdfReader(Assembly.GetExecutingAssembly().GetManifestResourceStream("SignedReport.Template.pdf"));
        MemoryStream outputStream = new MemoryStream();

        PdfStamper stamper;

        public AttestationPdf()
        {
            stamper = PdfStamper.CreateSignature(reader, outputStream, '\0');
        }

        public void AddReport()
        {

        }

        public void AddSignature()
        {
            AddDate();

            ApplySignature();

            stamper.Close();
        }

        private void AddDate()
        {
            stamper.AcroFields.SetField("Date", DateTime.Today.ToShortDateString());
        }

        private void ApplySignature()
        {
            PdfSignatureAppearance appearance = stamper.SignatureAppearance;
            appearance.Reason = "";
            appearance.CertificationLevel = PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED;
            appearance.Location = Environment.MachineName;
            appearance.SignatureGraphic = Image.GetInstance(Assembly.GetExecutingAssembly().GetManifestResourceStream("SignedReport.signature.png"));
            appearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.GRAPHIC;
            appearance.SetVisibleSignature("Signature");

            AsymmetricCipherKeyPair keyPair = null;
            Oid signatureHashAlgorithm = null;
            List<Org.BouncyCastle.X509.X509Certificate> chain = new List<Org.BouncyCastle.X509.X509Certificate>(); 
            using (X509Store certStore = new X509Store(StoreName.My, StoreLocation.LocalMachine))
            {
                certStore.Open(OpenFlags.ReadOnly);
                foreach (var cert in certStore.Certificates)
                {
                    if (cert.HasPrivateKey)
                    {
                        // Get CN and Thumbprint from App.config
                        if (cert.SubjectName.Name.Replace(" ", "").Contains(@"CN=commonName")) 
                        {
                            // make sure when the certificate was loaded into the certificate store 
                            //that the allow export option was checked.
                            keyPair = DotNetUtilities.GetKeyPair(cert.PrivateKey);
                            signatureHashAlgorithm = cert.SignatureAlgorithm;
                            chain.Add(DotNetUtilities.FromX509Certificate(cert));
                        }
                    }
                }
            }
            appearance.Certificate = chain[0];
            appearance.SignDate = DateTime.Now;

            IExternalSignature exSig = new PrivateKeySignature(keyPair.Private, "SHA-256");
            MakeSignature.SignDetached(appearance, exSig, chain, null, null, null, 0, CryptoStandard.CMS);
        }

        public void SaveAs(string filePath)
        {
            using (FileStream file = new FileStream(filePath, FileMode.Create, FileAccess.Write))
            {
                byte[] output = outputStream.ToArray();
                file.Write(output, 0, output.Length);
            }
        }

        #region IDisposable Support
        private bool disposedValue = false; // To detect redundant calls

        protected virtual void Dispose(bool disposing)
        {
            if (!disposedValue)
            {
                if (disposing)
                {
                    // TODO: dispose managed state (managed objects).
                    stamper.Dispose();
                    reader.Dispose();
                    outputStream.Dispose();
                }

                // TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
                // TODO: set large fields to null.

                disposedValue = true;
            }
        }

        // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
        // ~AttestationPdf() {
        //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
        //   Dispose(false);
        // }

        // This code added to correctly implement the disposable pattern.
        public void Dispose()
        {
            // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
            Dispose(true);
            // TODO: uncomment the following line if the finalizer is overridden above.
            // GC.SuppressFinalize(this);
        }
        #endregion
    }
}