First of all paganism itself is really not a religion. There is no such thing as the doctrine of paganism. In fact we have to remember that it's the Christians who use the term pagan to define those people who are not Christians.

When Christianity became generally accepted in the towns and cities of the empire, paganus was used to refer to a villager who continued to worship the old gods. Christians used the term for anyone not of their faith or of the Jewish faith. The word in Old English for such a person was what is now heathen.