I programmed the next Macro and works fine.

Sub ClearBookmarks()
'
' ClearBookmarks Macro
' Macro grabada el 01/12/2004 por Armando Szapiro
'
   Dim intNumBookmarks As Integer
   intNumBookmarks = ActiveDocument.Bookmarks.Count
   Dim ToDelete(intNumBookmarks)
   ActiveWindow.View.ShowFieldCodes = True

   For i = 1 To intNumBookmarks
       nombre = ActiveDocument.Bookmarks(i).Name

       Selection.HomeKey Unit:=wdStory
       Selection.Find.ClearFormatting
       With Selection.Find
           .Text = nombre
           .Replacement.Text = ""
           .Forward = True
           .Wrap = wdFindAsk
           .Format = False
           .MatchCase = False
           .MatchWholeWord = False
           .MatchKashida = False
           .MatchDiacritics = False
           .MatchAlefHamza = False
           .MatchControl = False
           .MatchWildcards = False
           .MatchSoundsLike = False
           .MatchAllWordForms = False
       End With
       If Not Selection.Find.Execute Then
           d = d + 1
           ToDelete(d) = nombre
       End If
   Next i
   If d > 0 Then
       For i = d To 1 Step -1

           ActiveDocument.Bookmarks(ToDelete(i)).Delete

       Next i
   End If

End Sub