Window.document it is the property in vb 6.0
No it isn't. It's the property of a HTML page loaded in the webbrowser control.
In VB.NET WebBrowser.Document
Gets the Document object that represents the hosted HTML page
and that's the same as what Window.document did in VB6. WebBrowser.Document has GetElementById() method to access HTML document's DOM. So, what you want to do with VB.NET that you did with VB6?