so funktionierts..

Sub SetzungenBookmark(ByVal txtSuch As String, ByVal txtErsetz As String)

    With Selection.Find
    .Text = txtSuch
        .Forward = True
        .Wrap = wdFindContinue
        .Format = False
        .MatchCase = False
        .MatchWholeWord = False
        .MatchWildcards = False
        .MatchSoundsLike = False
        .MatchAllWordForms = False
        .Execute
    End With
     
     If Selection.Find.found Then
      Selection.Delete
      ActiveDocument.Bookmarks.Add Name:=txtErsetz
      Selection.Collapse direction:=wdCollapseEnd
     End If
    
End Sub