void sweepKids(PdfObject obj) {
        PdfObject oo = PdfReader.killIndirect(obj);
        if (oo == null || !oo.isDictionary())
            return;
        PdfDictionary dic = (PdfDictionary)oo;
        PdfArray kids = (PdfArray)PdfReader.killIndirect(dic.get(PdfName.KIDS));
        if (kids == null)
            return;
        for (int k = 0; k < kids.size(); ++k) {
            sweepKids(kids.getPdfObject(k));
        }
    }