Batch (Bulk) PDF Digital Signature in C#

static void BatchPdfSignature(string sourceFolder, string destFolder)
      PdfSignature ps = new PdfSignature("");

      //Load the certificate from Microsoft Store. 
      //The smart card or USB token certificates are usually available on Microsoft Certificate Store (start - run - certmgr.msc).
      //If the smart card certificate not appears on Microsoft Certificate Store it cannot be used by the library
       cs.DigitalSignatureCertificate = DigitalCertificate.LoadCertificate(false, DigitalCertificateSearchCriteria.CommonNameCN, "Certificate Name");

      //The smart card PIN dialog can be bypassed for some smart cards/USB Tokens. 
      //ATTENTION: This feature will NOT work for all available smart card/USB Tokens becauase of the drivers or other security measures.
      DigitalCertificate.SmartCardPin = "123456";

      System.IO.DirectoryInfo di;
      System.IO.FileInfo[] rgFiles;
      //get the pdf files from the folder
      di = new System.IO.DirectoryInfo(sourceFolder);
      //select only the PDF files
      rgFiles = di.GetFiles("*.pdf");
      Console.WriteLine("Number of PDF files: " + rgFiles.Length.ToString());

      foreach (FileInfo fi in rgFiles)
          //for readonly files
          fi.Attributes = FileAttributes.Normal;
          //load the PDF document
          ps.LoadPdfDocument(sourceFolder + fi.Name);
          //write the signed file
          File.WriteAllBytes(destFolder + fi.Name, ps.ApplyDigitalSignature());

static void Main(string[] args)
    //digitally sign all pdf files available on the source_folder
    BatchPdfSignature("d:\\source_folder\\", "d:\\destination_folder\\");

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