java从一个pdf中取出指定页生成一个新的pdf

public static void partitionPdfFile(String pdfFile,
                                        String newFile, int from, int end) {
        Document document = null;
        PdfCopy copy = null;
        try {
            PdfReader reader = new PdfReader(pdfFile);
            int n = reader.getNumberOfPages();
            if (end == 0) {
                end = n;
            }
            
            document = new Document(reader.getPageSize(1));
            copy = new PdfCopy(document, new FileOutputStream(newFile));
            document.open();
            for (int j = from; j <= end; j++) {
                document.newPage();
                PdfImportedPage page = copy.getImportedPage(reader, j);
                copy.addPage(page);
            }
            document.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }