Affecto.Pdf.Toolkit.CertificateHelper.GetSigningCertificates C# (CSharp) Method

        public static SigningCertificates GetSigningCertificates(IDigitalSignatureCertificateSelector certificateSelector)
        {
            SigningCertificates signingCertificates = new SigningCertificates();

            X509CertificateParser parser = new X509CertificateParser();
            X509Store x509Store = new X509Store(StoreLocation.CurrentUser);
            x509Store.Open(OpenFlags.ReadOnly);

            X509Certificate2Collection validCertificates = FindDigitalSignatureCertificates(x509Store);

            signingCertificates.X509Certificate2 = certificateSelector.SelectCertificate(validCertificates.Cast<X509Certificate2>());
            signingCertificates.X509Certificate = parser.ReadCertificate(signingCertificates.X509Certificate2.Export(X509ContentType.Cert));
            signingCertificates.FinalChain = CreateChain(signingCertificates.X509Certificate, signingCertificates.X509Certificate2, parser);            

            return signingCertificates;
        }

        public static string SignFile(string fileName, PdfSignatureParameters parameters, IDigitalSignatureCertificateSelector certificateSelector)
        {
            if (string.IsNullOrWhiteSpace(fileName))
            {
                throw new ArgumentException("Filename must be given", nameof(fileName));
            }
            if (!File.Exists(fileName))
            {
                throw new ArgumentException($"File {fileName} not found.");
            }
            if (parameters == null)
            {
                throw new ArgumentNullException(nameof(parameters));
            }
            if (certificateSelector == null)
            {
                throw new ArgumentNullException(nameof(certificateSelector));
            }

            string tempPath = string.Empty;

            try
            {
                tempPath = GetTempPath(parameters.TempFolderPath);

                string targetFilePath = GetTargetFilePath(parameters.TempFolderPath, parameters.TargetFilePath);

                var signingCertificates = CertificateHelper.GetSigningCertificates(certificateSelector);

                // Two clients for checking certificate revocation
                // * Online Certificate Status Protocol (OCSP) client
                // * Certificate Revocation Lists (CRL) client with online checking
                // Certificate will be checked when the signature is made
                OcspClientBouncyCastle oscpClient = new OcspClientBouncyCastle(null);
                List <ICrlClient>      clrClients = new List <ICrlClient> {
                    new CrlClientOnline(signingCertificates.FinalChain)
                };

                using (FileStream targetFileStream = new FileStream(targetFilePath, FileMode.Create))
                    using (PdfReader reader = new PdfReader(fileName))
                        using (PdfStamper stamper = PdfStamper.CreateSignature(reader, targetFileStream, '0', tempPath, true))
                        {
                            PdfSignatureAppearance appearance = GetPdfSignatureAppearance(signingCertificates, stamper, reader, parameters);

                            CreateSignature(signingCertificates, appearance, clrClients, oscpClient);
                        }

                return(targetFilePath);
            }
            finally
            {
                try
                {
                    if (!string.IsNullOrWhiteSpace(tempPath) && File.Exists(tempPath))
                    {
                        File.Delete(tempPath);
                    }
                }
                catch (Exception)
                {
                }
            }
        }