Is it forbidden to exchange an educational booklet (that has been authored) for another booklet? If so, what is its expiation?

If the school does not authorize giving the course material to the page owner, then it is not permissible, because it is an infringement on their right. The expiation for this is repentance to Allah and seeking the school's forgiveness. If they forgive you, then there is nothing upon you. Otherwise, you must reconcile with them regarding their right. Giving charity on their behalf is not sufficient unless you are unable to seek their forgiveness or return their right.