public byte[] Sign(string thumbprint, byte[] bytes, int signatureFieldNumber, bool silent = true,
            CancellationToken token = default)
        {
            var certCollection = _store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, false);

            if (!certCollection.Any())
                throw new CryptoProException($"Не найден сертификат {thumbprint}");

            var cert = certCollection[0];

            
            if (cert is null)
                throw new CryptoProException($"Не найден сертификат {thumbprint}");

            using (MemoryStream output = new())
            {
                using (var reader = new PdfReader(bytes))
                {
                    PdfStamper st = PdfStamper.CreateSignature(reader, output, '\0', null, true);

                    PdfSignatureAppearance sap = st.SignatureAppearance;

                    // Формируем штампик
                    X509CertificateParser parser = new X509CertificateParser();
                    Org.BouncyCastle.X509.X509Certificate[] chain = new Org.BouncyCastle.X509.X509Certificate[] {
                        parser.ReadCertificate(cert.RawData)
                    };

                    sap.Certificate = parser.ReadCertificate(cert.RawData);
                    sap.Layer2Text = GetSignText(cert);
                    sap.Layer2Font = GetFont();
                    sap.Image = GetImage();
                    sap.SetVisibleSignature(GetRectangle(signatureFieldNumber), reader.NumberOfPages,
                        signatureFieldNumber.ToString());

                    IExternalSignature exSig = new MainSignature(cert.PrivateKey);

                    MakeSignature.SignDetached(sap, exSig, chain, null, null, null, 0, CryptoStandard.CMS);

                    return output.ToArray();
                }
            }
        }

public class MainSignature : IExternalSignature
        {
            private AsymmetricAlgorithm _alg;
            public MainSignature(AsymmetricAlgorithm alg)
            {
                _alg = alg;
            }

            public byte[] Sign(byte[] message)
            {
                var privateKey = _alg as Gost3410_2012_256CryptoServiceProvider;

                return privateKey.SignData(
                    message,
                    CpHashAlgorithmName.Gost3411_2012_256);
            }

            public String GetHashAlgorithm()
            {
                return "GOST3411";
            }

            public String GetEncryptionAlgorithm()
            {
                return "RSA";
            }
        }