vb.net select an item of a datatable linked to a listbox and show a http page offline in webbrowser control

I wanna have confirmations, if this part of code works to select an item for a datatable linked with a listbox for select a item from the index of datatable.

If ListBox1.SelectedIndex = 0 Then

and after open a web page (a offline webpage saved in local) if that index is selected, , into the webbrowser control, on the actual form(but doesn't appear nothing).

WebBrowser1.Document.Write(IO.File.ReadAllText("test.html"))

Also, it's possible to put the webbrowser in offline mode, because it need to open offline web pages ?