public static void splitPDFByBookmarks(String pdf, String outputFolder){
        try
        {
            PdfReader reader = new PdfReader(pdf);
            //List of bookmarks: each bookmark is a map with values for title, page, etc
            List<HashMap> bookmarks = SimpleBookmark.getBookmark(reader);
            for(int i=0; i<bookmarks.size(); i++){
                HashMap bm = bookmarks.get(i);
                HashMap nextBM = i==bookmarks.size()-1 ? null : bookmarks.get(i+1);
                //In my case I needed to split the title string
                String title = ((String)bm.get("Title")).split(" ")[2];

                log.debug("Titel: " + title);
                String startPage = ((String)bm.get("Page")).split(" ")[0];
                String startPageNextBM = nextBM==null ? "" + (reader.getNumberOfPages() + 1) : ((String)nextBM.get("Page")).split(" ")[0];
                log.debug("Page: " + startPage);
                log.debug("------------------");
                extractBookmarkToPDF(reader, Integer.valueOf(startPage), Integer.valueOf(startPageNextBM), title + ".pdf",outputFolder);
            }
        }
        catch (IOException e)
        {
            log.error(e.getMessage());
        }
    }

    private static void extractBookmarkToPDF(PdfReader reader, int pageFrom, int pageTo, String outputName, String outputFolder){
        Document document = new Document();
        OutputStream os = null;

        try{
            os = new FileOutputStream(outputFolder + outputName);

            // Create a writer for the outputstream
            PdfWriter writer = PdfWriter.getInstance(document, os);
            document.open();
            PdfContentByte cb = writer.getDirectContent(); // Holds the PDF data
            PdfImportedPage page;

            while(pageFrom < pageTo) {
                document.newPage();
                page = writer.getImportedPage(reader, pageFrom);
                cb.addTemplate(page, 0, 0);
                pageFrom++;
            }

            os.flush();
            document.close();
            os.close();
        }catch(Exception ex){
            log.error(ex.getMessage());
        }finally {
            if (document.isOpen())
                document.close();
            try {
                if (os != null)
                    os.close();
            } catch (IOException ioe) {
                log.error(ioe.getMessage());
            }
        }
    }

Regards,
Prem