this my code
string certBase64 = Encoding.UTF8.GetString(Convert.FromBase64String(currentCompliance.binarySecurityToken));
byte\[\] privateKeyBytes = Convert.FromBase64String(currentCompliance.privateKey_Base64);
string privateKeyPem = Encoding.UTF8.GetString(privateKeyBytes);
EInvoiceSigner signer = new EInvoiceSigner();
SignResult result = signer.SignDocument(xmlDocument, certBase64, privateKeyPem);