So what would be the best way to test which file has been opened ?
I think you are confusing ActiveWorkbook with Opened workbook and New Workbook.
The ActiveWorkbook is merely the one you are looking at on the screen. It doesn't matter if it is a CSV file, a TXT file, an XLSM, XLST, XLSX, XLSB, or a brand new file that has never been saved.
If you Open a Workbook, it will have an Extension in its' name. Therefor you can usually tell the difference between any saved workbook and a new unsaved workbook programmatically with
If Instr("Name of Book", ".") <> 0 Then 'Book has been saved.