void addPageOffsetToField(Map<String, AcroFields.Item> fd, int pageOffset) {
        if (pageOffset == 0)
            return;
        for (AcroFields.Item item: fd.values()) {
            for (int k = 0; k < item.size(); ++k) {
                int p = item.getPage(k).intValue();
                item.forcePage(k, p + pageOffset);
            }
        }
    }