* @param extractData the extraction data to add metadata to
     */
    protected void extractMetadata(final PDDocument document, final ExtractData extractData) {
        final PDDocumentInformation info = document.getDocumentInformation();
        if (info == null) {
            return;
        }

        for (final String key : info.getMetadataKeys()) {
            final String value = info.getCustomMetadataValue(key);