说明：  这个东西是模拟打印机，可以直接打印到pdf文件里面。除了平常需要外，当你测试打印程序却没有打印机时，这个东西用处很大。
(this thing is simulated printer can print directly to the pdf file inside. In addition to the normal needs, when you test procedures did not print printers, this thing very useful.)