//xml轉為string

        public string ConvertXmlToString(XmlDocument xmlDoc)

        {
            MemoryStream stream = new MemoryStream();
            XmlTextWriter writer = new XmlTextWriter(stream, null);
            writer.Formatting = Formatting.Indented; xmlDoc.Save(writer);
            StreamReader sr = new StreamReader(stream, System.Text.Encoding.UTF8);
            stream.Position = 0;
            string xmlString = sr.ReadToEnd();
            sr.Close();
            stream.Close();
            return xmlString;

        } 

//string轉為xml

            XmlDocument xmlDoc = new XmlDocument();

            xmlDoc.LoadXml(strContent);

//從本地檔案讀取xml

            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(@"D:\test.xml");