Assuming I have a book on a table. First, there is gravitational force acting on the book, which causes the book to also exert the same amount of force on the Earth. Now, the table will also exert a normal force on the book to counteract the gravitational force (weight of the book). However, there must be a reaction force to the normal force isn't it? If so, how can the book be possibly staying on the table if it exerts another reaction force on the table?
This sentence "However, there must be a reaction force to the normal force isn't it?" is about a force on the table and not the book.
The book has the gravitational pull of the earth acting on it and the normal reaction force from the table. Those two balance and the book stays on the table.