private void Encrypt()
        {
            string fileToEncrypt = @"D:\SendFNS_new\test.txt";
            byte[] msg = File.ReadAllBytes(fileToEncrypt);
            ContentInfo contentInfo = new ContentInfo(msg);
            EnvelopedCms envelopedCms = new EnvelopedCms(contentInfo);

            X509Certificate2 cert = new X509Certificate2(@"D:\SendFNS_new\b383c9e334a8fab3c324d52d0e28166fe894c1eb.pem");

            CmsRecipient recip1 = new CmsRecipient(cert);
            envelopedCms.Encrypt(recip1);

            byte[] encryptedData = envelopedCms.Encode();

            File.WriteAllBytes(fileToEncrypt + ".enc", encryptedData);
        }