How about

Dim oRng As Range
    Set oRng = ActiveDocument.Range
    With oRng.Find
        .Highlight = True
        Do While .Execute
            With oRng
                .InsertBefore "("
                .InsertAfter ")"
                .HighlightColorIndex = wdNoHighlight
                .Collapse 0
            End With
        Set oRng = Nothing
    End With