When a perfectly non elastic object (let's say a book) is dropped on the ground, it's kinetic energy from the fall is transformed into heat and sound.
Now, if W = Fs, the work done by the normal reaction force on the book is zero since the book does not move after it hits the ground.
My question is how can the kinetic energy be transformed into other forms if no work is being done on the book? Is transformation of energy into different forms unrelated to work?
The work energy theorem assumes only one force, or the resultant of many. If you add other forces, like a friction, that will stop the moving object. In the case of the book it is the normal force that stops it and the book's deformation eventual gets dissipated into heat and deformation energy. This violates the macroscopic conservation of energy, but not the microscopic one, and we know all objects are compose of microscopic elements (atoms, electrons), so conservation of energy is never really violated, it only apparent on macroscopic objects.
"Perfectly non elastic objects" the size of a book do not exist, so nobody knows what would happen if you dropped one on the ground. (In classical mechanics, there is the concept of "point particles," but we know that very small objects in the real world behave according to quantum mechanics not classical mechanics, and point particles also do not exist!)
For real books, the sound is created by movement of the air around the book. In particular, when the book is very close to the ground all the air between the book and the ground has to be pushed out of the way, and the sideways velocity of the air is much greater than the downwards velocity of the book. (Suppose the length and width of the book is 100mm, and it is 1mm above the ground. In the time it takes to fall the final 1mm, the air near to the center of the book has to move 50mm to reach the edge of the book, so it has to travel 50 times faster than the book.)
This rapid air movement creates a pressure wave which spreads out through the air, and which you hear as "sound".
The book is made of atoms, which (unless the book is at a temperature of absolute zero) are all moving around their "average" positions in the solid material. The energy in those vibrations are described as "heat energy" and if it increases, we say that the "temperature" of the book increases.
When the book hits the ground, the average kinetic energy of the book moving downwards is transferred to the atomic vibrations, and therefore becomes additional heat energy and increases the temperature of the book.
The difference between an inelastic collision and an elastic collision is that in an elastic collision, some of the additional heat energy is transferred back into a global motion of the book, as it "bounces" after the collision. Without attempting to explain the details, you can imagine that if the atoms and molecules in the object are arranged in a regular pattern (like a crystal) this is more likely to happen than if the arrangement is irregular, and therefore some materials are more elastic than others.
