XDocument转XmlDocument ，XmlDocument转XDocument 静态扩展方法

//XmlDocument转XDocument

public static class XmlDocumentExtensions
    {
        public static XDocument ToXDocument(this XmlDocument document)
        {
            return document.ToXDocument(LoadOptions.None);
        }

        public static XDocument ToXDocument(this XmlDocument document, LoadOptions options)
        {
            using (XmlNodeReader reader = new XmlNodeReader(document))
            {
                return XDocument.Load(reader, options);
            }
        }
    }

//XDocument转XmlDocument 

var doc = new XmlDocument();
doc.LoadXml(xdoc.Document.ToString());