How Do I Get An An Xml On Page Load And Save In An Variable ?

Why do you need to store entire XML in a variable? Instead you can create a function to read XML File. If you still want to do so, use:

XDocument doc = XDocument.Load("XMLFile1.xml" );

[Update]

//Calling a function
XDocument doc = MyFunction();

//Function Here
private XDocument MyFunction()
{
    return  XDocument.Load("XMLFile1.xml" );
}

--Amy