protected void readDocObjPartial() throws IOException {
        xrefObj = new ArrayList<PdfObject>(xref.length / 2);
        xrefObj.addAll(Collections.<PdfObject>nCopies(xref.length / 2, null));
        readDecryptedDocObj();
        if (objStmToOffset != null) {
            long keys[] = objStmToOffset.getKeys();
            for (int k = 0; k < keys.length; ++k) {
                long n = keys[k];
                objStmToOffset.put(n, xref[(int)(n * 2)]);
                xref[(int)(n * 2)] = -1;
            }
        }
    }