软件输出打印页码功能，该页码会将PDF打印成一本书，一张纸打印四页，一次打印若干页，先打印正面，再打印反面，然后讲所有页对折，用剪刀剪开，就形成了书的样式(bookpage software.the aim is to get the page numbers which make the printing page can be made to a book which is made by some paper folded in half)