expression.WindowNumber
expression Required. An expression that returns a Window object.
Remarks
Use the Index property to return the number of the specified window in the Windows collection.
Example
This example retrieves the window number of the active window, opens a new window, and then activates the original window.
Sub WinNum()
Dim lwindowNum As Long
lwindowNum = ActiveDocument.ActiveWindow.WindowNumber
NewWindow
ActiveDocument.Windows(lwindowNum).Activate
End Sub