procedure TForm1.Button1Click(Sender: TObject); 
begin 
  Webbrowser1.Navigate('file:///c:/test.txt'); 
end; 

procedure TForm1.WebBrowser1DocumentComplete(Sender: TObject; 
  const pDisp: IDispatch; var URL: OleVariant); 
begin 
  if Webbrowser1.Oleobject.Document.Location.Protocol = 'file:' then 
  begin 
    label1.Caption := 'The file is on a local drive!' 
    // label1.Caption := 'Das File befindet sich auf einer lokalen Harddisk!' 
  end; 
end;