The lock is on the first page of the book. According to relevant data, folding, also known as folding, refers to the extended folding part of the book cover, that is, the position of the redundant folding on the first page. At present, many books are equipped with a folder, that is, the cover is folded, about 70 to 100 mm, and the folder will basically contain the author's photo, author profile, QR code, slogan, series of small covers, organization profile and other contents, which can not only promote the purpose but also help readers better understand the contents of the book.