That is infringement. Many of the flipbook makers cannot allow you to do some setting for protection or many people have no copy awareness upon their flipbook. Here is one PDF to flipbook
Why do we need to protect our flipbook?
2. Privacy:Here is one condition that all of your contents may include some secret parts which you only want to share with some of the friends. In this time you can choose to hide parts of the contents and only show them to your friends.