In response to the request to use a website (instead of a file), the pertinent code is shown below. Note that you will need to replace "www.somewebsite.com" with the website page that you want to capture the source code (HTML, for example) from.
Dim webclient As System.Net.WebClient = New System.Net.WebClient
Dim url As String = "http://www.somewebsite.com"
Dim myHTML As String = webclient.DownloadString(url)