如何使用Java加密PDF？

这就是我用它来加密它：

public byte[] cryptograph(Key key,byte[] content){
    Cipher cipher;
    byte[] cryptograph = null;
    try {
        cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE,key);
        cryptograph = cipher.doFinal(content);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return cryptograph;

}

这要解密它：

public byte[] decrypt(Key key,byte[] textCryp){
    Cipher cipher;
    byte[] decrypted = null;
    try {
        cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE,key);
        decrypted = cipher.doFinal(textCryp);
    } catch (Exception e) {         
        e.printStackTrace();
    } 

    return decrypted;
}

更新：

这是我用来读取文件的内容：

public byte[] getFile(){
    byte[] content = null;
    try {
        InputStream is = new FileInputStream("test.pdf");
        BufferedInputStream vf = new BufferedInputStream(is);
        content = new byte[vf.available()];
        vf.read(content);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return content;
}

用它来重写文件

public static void saveDecrypt(byte[] bytes) throws IOException{
        Document doc=new Document();
        try {
            PdfWriter.getInstance(doc,new FileOutputStream("fileDecrypted.pdf"));
            doc.open(); 
            doc.add(new Paragraph(new String(bytes)));
            doc.close();
        } catch (DocumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }