Document_Open() does not work in other files - vba

Question

I am writing a VBA project containing 1 module (m1) and 1 userform (uf).
In "ThisDocument" I am calling a public sub from "m1" that initializes a collection I then refer to in the userform. This works perfectly fine until I deploy this project to other files.
I save the file as a .dotm in the %Appdata%/Microsoft/word/startup folder so I can use the project in all of my word files. But as soon as I try to use my project in other files the userform opens itself as designed but the collection is empty.
What could be the problem here?
Manually calling the initialization method from the userform works fine.
'----------------------------------------------ThisDocument
Private Sub Document_Open()
initBetaCollection
End Sub
'----------------------------------------------m1
Option Explicit
Public beta As Collection
Sub initBetaCollection()
Set beta = New Collection
beta.Add Array("0041", "A"), Key:="0041"
'...
End Sub
'----------------------------------------------uf
Option Explicit
Private Sub txtSearch_Change()
Dim arr As Variant
Dim search As String
'Defining the textinput as "search"
search = txtSearch.Value
For Each arr In beta
If search <> "" Then 'No empty search field
If arr(1) Like "*" & search & "*" Then 'Match found
lbResults.AddItem arr(0)
End If
End If
Next
End Sub
I get the: Run Time Error '424' object required

Answer 1

The problem with using Document_Open in the ThisDocument class or a macro named AutoOpen in a regular module is that both execute specifically for this document (or documents created from the template), only.
In order to have an application-level event, that fires for all documents opened, it's necessary to work with application-level events.
For this, first a class module is required. In the class module, the following code is needed:
'Class module named: Class1
Public WithEvents app As Word.Application
Private Sub app_DocumentOpen(ByVal Doc As Document)
'MsgBox Doc.FullName & ": on Open"
'Code here that should fire when a document is opened
'If something needs to be done with this document, use
'the Doc parameter passed to the event, don't try to use ActiveDocument
End Sub
Then, in a regular module, an AutoExec macro can be used to initialize the class with event handling. (AutoExec: fires when Word starts and loads a template with a macro of this name.)
Option Explicit
Dim theApp As New Class1
Sub AutoExec()
'MsgBox "AutoExec"
Set theApp.app = Word.Application
End Sub
'Sub AutoOpen()
' MsgBox "Open in AutoOpen" - fires only for this document
'End Sub