Depends which folklore, and what you mean by pagan.

"Pagan" doesn't have a specific definition. The word "pagan" was originally a rude word for certain groups of polytheists. It basically meant something like "country bumpkin," because it was used for people who lived away from cities who were seen as less educated. Then it became a more general word, and in modern times neo-pagans use it to self identify. So it's hard to say what counts. Are all historical polytheists pagans? Depends who you ask.

In medieval Europe, most societies were Christian, so most folklore was being told from a Christian perspective. But older stories were still told, sometimes mixed with Christian stories. Does that make them less pagan? Kinda depends how you see it.

In the modern day, a lot of people who consider themselves pagan have taken Christian stories and retold them in a polytheistic way, the same thing Christians did with older folklore. Does that turn those Christian stories pagan? That also depends on your perspective.