Something

static string DocumentToText(XmlDocument document)
        {
            MemoryStream stream = new MemoryStream();           
            XmlTextWriter writer = new XmlTextWriter(stream, Encoding.UTF8);              
            writer.Formatting = Formatting.Indented;
          
            writer.WriteStartDocument();

            document.WriteTo(writer);    
    
            writer.WriteEndDocument();
            writer.Flush();

            UTF8Encoding encoding = new UTF8Encoding();
            return encoding.GetString(stream.ToArray());           
        }