Is it permissible to print books and handouts without inquiring about how to obtain them?

You are permitted to print documents without inquiring from their owners how they obtained them, for the fundamental principle is that whatever is in people's possession belongs to them, and ignorance of the true situation does not affect this. Sheikh al-Islam Ibn Taymiyyah stated that the basic principle regarding what is in a Muslim's possession is that it belongs to him, and that property whose status is unknown is considered as non-existent. Transactions are permissible concerning all properties in the possession of Muslims, Jews, and Christians, unless it is known to have been usurped. Investigating and asking customers how they acquired what they possess might lead to hardship.