Window.Height (Word)

Returns or sets the height of the window (in points).

You cannot set this property if the window is maximized or minimized. Use the UsableHeight property of the Application object to determine the maximum size for the window. Use the WindowState property to determine the window state.

With ActiveDocument.ActiveWindow 
 .WindowState = wdWindowStateNormal 
 .Height = Application.UsableHeight 
End With