Sub SubtractOne()
Application.ScreenUpdating = False
Dim i As Long, Rng As Range
With Selection
  If .Information(wdWithInTable) Then
    For i = 1 To .Rows.Count
      With .Columns(1).Cells(i)
        Set Rng = .Range
        With Rng
          .End = .End - 1
          If IsNumeric(.Text) Then .Text = .Text - 1
        End With
      End With
    Next
  End If
End With
Application.ScreenUpdating = True
End Sub