if (filename.toLowerCase().endsWith("pdf")) {
File file = new File(filename);
FileISBNExtractor fileISBNExtractor = new FileISBNExtractor();
fileISBNExtractor.setSearchMinBytes(30000);
fileISBNExtractor.getTextReaderFactory().setPreferredPdfExtractor(new PDFBoxTextExtractor());
ISBNCandidates isbnCandidates = fileISBNExtractor.getIsbnCandidates(file);
org.chabanois.isbn.extractor.ISBN extractedISBN = isbnCandidates.getHighestScoreISBN();
if (extractedISBN != null ) {
String s = extractedISBN.getIsbn();