private List<COSDictionary> findFileSpecs(COSDictionary cosDict) {
        Set<COSName> types = new HashSet<>();
        types.add(COSName.FILESPEC);
        return PDFDOMUtil.findType(cosDict, types, MAX_RECURSION_DEPTH);
    }
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