This example closes all windows except the active window.
With Application.Windows
    For i = 2 To .Count
        .Item(i).Close
    Next
End With
This example closes Pres1.ppt without saving changes.
With Application.Presentations("pres1.ppt")
    .Saved = True
    .Close
End With
This example closes all open presentations.
With Application.Presentations
    For i = .Count To 1 Step -1
        .Item(i).Close
    Next
End With