.net - Loading Html Page As Xml?

I use this to load html page by xml

Dim xmlDoc As New XmlDocument()
xmlDoc.Load(Server.MapPath("index.htm"))
Or
Dim xmldoc As XDocument
xmldoc = XDocument.Load(Server.MapPath("index.htm"))

but i got some errors like :

Expecting an internal subset or the end of the DOCTYPE declaration. Line 2, position 14.'>' is an unexpected token. The expected token is '"' or '''. Line 1, position 62.Expecting an internal subset or the end of the DOCTYPE declaration. Line 5, position 20.

all these errors came to me when i solve one another one show up.

i'm asking do i use the perfect way to load this file or is there another way for that?