What is the ruling on purchasing foreign books that some bookstores have photocopied and sold to students at low prices, without the knowledge of the publishing houses that hold the copyrights? Is it permissible or forbidden?

If the authors of the books stipulate the preservation of copyrights, then libraries are not permitted to photocopy them for profit and trade without their permission, as this constitutes an infringement of their rights. Likewise, it is not permissible to purchase these photocopied books without permission, as this would be a participation in the infringement.