void extractBookmarkText() throws SAXException, IOException, TikaException {
        PDDocumentOutline outline = document.getDocumentCatalog().getDocumentOutline();
        if (outline != null) {
            Set<COSObjectable> seen = new HashSet<>();
            extractBookmarkText(outline, seen, 0);
        }
    }
Format used for signature dates
TODO Make this thread-safe
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-pdf-module/src/main/java/org/apache/tika/parser/pdf/AbstractPDF2XHTML.java