Secret message hidden in a book
To achieve the goal here, we have to write a text (or choose a text written by somebody else). In this text we have to locate the words that can form the message we want to send. Once we locate the words, we need to find the specific piece of paper that has pre-cut holes and to lay it on top of a specific page in order to reveal a set of words or letters. A previous riddle could be to find out the title of the book and the number of the page that contains the message.