Is working as a proofreader for books whose authors are atheists, or books that contain immoral scenes and incitement to suicide, permissible or forbidden, and is the money earned from it permissible or forbidden?

The basic principle is that linguistic proofreading is permissible, and earning from it is lawful as long as the books or research are beneficial and permissible. However, linguistic proofreading for materials that promote misguidance or immorality is not permissible, as it involves cooperation in sin and transgression, unless it is for a valid purpose, such as studying them in order to refute them. The mere fact that the author of a book is an atheist or deviant does not prevent proofreading their book if it is beneficial and permissible.