Is it permissible to acquire information from paid training courses that has been shared for free by an unknown person who is not its owner?

If you do not have knowledge or a strong presumption that the courses are published without the permission of their owners, then there is no harm in benefiting from them. However, if you know or strongly presume that they are, then you are not permitted to benefit from them. You must repent and seek forgiveness from their owners. There is no harm in benefiting from information you have previously learned.