private static XmlDocument SignXmlDocument(Stream xmlStream, string guid)
        {
            X509Store store = new X509Store("My", StoreLocation.CurrentUser);
            store.Open(OpenFlags.OpenExistingOnly | OpenFlags.ReadOnly);

            // NUC RK (RSA) certificate imported to my PC - Личный сертификаты
            X509Certificate2 foundCertificate = store.Certificates[0];

            // load xml from disk preserving whitespaces
            XmlDocument xmlDocument = new XmlDocument { PreserveWhitespace = true };
            xmlDocument.Load(xmlStream);
            
            // create signed xml with a same-document reference containing an enveloped-signature transform
            SignedXml signedXml = new SignedXml(xmlDocument) { SigningKey = foundCertificate.PrivateKey };
            Reference reference = new Reference();
            XmlDsigEnvelopedSignatureTransform env = new XmlDsigEnvelopedSignatureTransform();
            XmlDsigC14NWithCommentsTransform c14 = new XmlDsigC14NWithCommentsTransform();
            reference.AddTransform(env);
            reference.AddTransform(c14);
            reference.Uri = "#"+guid;
            signedXml.AddReference(reference);

            // embed public key information for signature validation purposes
            KeyInfo keyInfo = new KeyInfo();
            KeyInfoX509Data keyInfoX509Data = new KeyInfoX509Data(foundCertificate, X509IncludeOption.ExcludeRoot);
            keyInfo.AddClause(keyInfoX509Data);
            signedXml.KeyInfo = keyInfo;

            // compute and retreive the signature xml
            signedXml.ComputeSignature();
            XmlElement xmldsigXmlElement = signedXml.GetXml();

            // insert the signature xml into the xml document as first child of the root element
            xmlDocument.GetElementsByTagName("soap:Header").Item(0).PrependChild(xmlDocument.ImportNode(xmldsigXmlElement, true));

            return xmlDocument;
        }