How to know if a file (notepad) is open?

Hello!

How to now if Notepad, let's say test.txt, is open or not?

Also how to close it or any file.

Around internet there are a lot of virtual things as close notepad with VBA,
however, so far I haven't found any working code,
this looks quite nice:

Dim fileToOpen As String
  fileToOpen = "C:\test.txt"
  Open fileToOpen For Output As #1
     Sleep 1000
  Close #1
End Sub

However, it does not open test.txt so I don't now could it close it also.

The big question is as the title suggest, how can one know if test.txt is already open?

regards
keymuu