I have read within the questions and used the command to have a message box
show automatically when a file is opened.

Start VBA
In the ThisWorkBook module, enter:
Private Sub Workbook_Open()
MsgBox ("Blah Blah Blah")
End Sub

However, its not quite foolproof as the user has an option to enable or
disable the macro at file open stage. If they disable the macro - they don't
see the message.
Is there any other way of showing a message on file open that does not give
the user an option to disable it and therefore miss the message.

Thanks

Ron