Is it permissible to download free textbooks from the internet when paid versions of them exist, and does the ruling differ based on one's financial ability to purchase them, and what is the ruling on one who publishes these books?

Copyrights, inventions, and innovations are protected by Islamic law, and it is not permissible to infringe upon them. Therefore, it is not permissible to download or publish books except with the permission of their owners. However, some scholars have permitted this for non-commercial personal use, especially for students of knowledge who cannot obtain original copies.