I am trying to call a WebService and it requires me to prepare an XML digital signature interface. I came across this website and it shows how to sign an XML document. My problem now is that I do not create the XML document myself. My code is as follows: string myResult; GenericWS.ServicesService a = new GenericWS.ServicesService(); GenericWS.Service2 b = new GenericWS.Service2(); b.Something = "3"; X509Certificate cert = X509Certificate.CreateFromCertFile("C:\\somepath\\somecert.cer"); a.ClientCertificates.Add(cert); ServicePointManager.ServerCertificateValidationCallback = delegate (object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; }; myResult= a.WSRequest(b).WSReturnValue.ToString(); Label1.Text = myResult; Basically, the WSRequest() will generate the body of the SOAP message. However, in order to sign the SOAP message, I need to pass in the XML file that needs to be signed. I tried to serialize the object and cast it as XML and pass it into the signature interface but I do not have another method that I can invoke to call the webmethod. Is there any other solution?