' Source point
' https://social.msdn.microsoft.com/Forums/vstudio/en-US/a10c6bcd-4745-4e07-a02e-3d98f5b6e941/display-all-open-excel-workbooks-in-a-listbox-multiple-processes
'

Option Explicit

Const OBJID_NATIVEOM = &HFFFFFFF0

Const E_NOINTERFACE = &H80004002
Const E_INVALIDARG = &H80070057
Const DISP_E_MEMBERNOTFOUND = &H80020003
Const E_NOTIMPL = &H80004001
Const E_OUTOFMEMORY = &H8007000E
Const E_FAIL = &H80004005
Const S_OK = &H0&
Const S_FALSE = &H1&

Private Declare Function GetDesktopWindow Lib "user32" () As Long

Private Declare Function EnumChildWindows Lib "user32" ( _
    ByVal hWndParent As Long, _
    ByVal lpEnumFunc As Long, _
    ByVal lParam As Long) As Long
    
Private Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" ( _
    ByVal Hwnd As Long, _
    ByVal lpString As String, _
    ByVal cch As Long) As Long
    
Private Declare Function GetWindowTextLength Lib "user32" Alias "GetWindowTextLengthA" ( _
    ByVal Hwnd As Long) As Long

Private Declare Function GetClassName Lib "user32.dll" Alias "GetClassNameA" ( _
    ByVal Hwnd As Long, _
    ByVal lpClassName As String, _
    ByVal nMaxCount As Long) As Long

Private Declare Function AccessibleObjectFromWindow Lib "oleacc" ( _
    ByVal Hwnd As Long, _
    ByVal dwId As Long, _
    ByRef riid As GUID, _
    ByRef ppvObject As Object) As Long

Private Type GUID
    Data1 As Long
    Data2 As Integer
    Data3 As Integer
    Data4(0 To 7) As Byte
End Type

' entry point
Sub Main()
    Call EnumChildWindows(GetDesktopWindow(), AddressOf EnumChildProc, ByVal 0&)
End Sub

Function EnumChildProc(ByVal Hwnd As Long, ByVal lParam As Long) As Long
    Dim txt As String
    Dim obj As Object
    Dim WordApp As Object
    
    Dim IID_IDispatch As GUID
    '["{00020400-0000-0000-C000-000000000046}"]
    With IID_IDispatch
       .Data1 = &H20400
       .Data4(0) = &HC0
       .Data4(7) = &H46
    End With
    
    Dim ClassName As String, Ret As Long
    ClassName = Space(255)
    Ret = GetClassName(Hwnd, ClassName, 255)
    ClassName = Left$(ClassName, Ret)
    
    'https://docs.microsoft.com/en-us/windows/win32/api/oleacc/nf-oleacc-accessibleobjectfromwindow
    If "_WwG" = ClassName Then
        Ret = AccessibleObjectFromWindow(Hwnd, OBJID_NATIVEOM, IID_IDispatch, obj)

        If S_OK = Ret Then
            txt = Space$(GetWindowTextLength(Hwnd) + 1)
            Call GetWindowText(Hwnd, txt, Len(txt))
            txt = Left$(txt, Len(txt) - 1)

            Debug.Print Hwnd, ClassName, txt
            ' obj is Window
            Set WordApp = obj.Application
            Debug.Print obj.Document.Content
            
            Set WordApp = Nothing
            Set obj = Nothing
        End If
    End If

    'continue enumeration
    EnumChildProc = 1
End Function