Описание тега xmldocument

XmlDocument is the original.NET type that represents an XML document. The more modern version is XDocument.

Use XmlDocument.LoadXml to load an XmlDocument from a string. Use one of the XmlDocument.Load methods to load from a file path or URL, Stream, TextReader, or XmlReader.

Using XmlDocument.Load with a string containing XML will lead to the common "Data at the root level is invalid" exception.