excel - Running vba code whenever a workbook is opened

I'm writing vba which manipulates data within a worksheet however I'm trying to make it run whenever a workbook is opened.

The problem I'm having is that due to the workbook (that the code needs to run on) is different/new every time, I need the auto_open code to be within a personal macro workbook.

Sub Auto_Open()
Dim bookname As String
Dim checkbook As String
Dim Workbook As Workbook
For Each Workbook In Application.Workbooks
bookname = Workbook.Name
checkbook = Left(bookname, 3)
   If checkbook = "EDN" Then
     Data_generator
     Application.DisplayAlerts = False
     ThisWorkbook.Save
     Application.DisplayAlerts = True
     Application.Quit
  Else
  End If
Next Workbook
End Sub

When this code runs it checks all open workbooks and sees if the first 3 letters of it are 'EDN', if it is then run the public sub called 'Data_generator', save it and quit. If it isn't check the next open workbook, etc.

When a file is opened from windows explorer, excel launches (with both the desired workbook and the personal macro workbook) however because excel opens the personal macro workbook first and runs the code before opening the desired workbook it doesn't find a workbook called 'EDN'.

If the above code is ran after both workbooks have opened then the code works as intended and cycles through each open workbook to see if there's one called 'EDN' (this was proved by putting a messagebox after the 'then' and running the code), if so run the sub.

I've proved this by putting a messagebox after the 'else', when this is done it displays the messagebox with the workbook I want, not open. After the message box is cleared, the workbook then opens.

Is there any way to make the desired workbook open first or any other work around for this?