But you see that's the problem, the book is inaccurate.
First of all there is no "Pagan religion". Pagan is an umbrella term that covers a wide variety of different religions. And by the 1400's Europe was firmly Christianized. There really weren't Pagans still running around in the woods by then.
Secondly, the Spanish Inquistion was never trying to ferret out Pagans or Witches. Their interest was in Christian heretics. In Spain there are transcripts of the Inquisition where someone claimed to be a Witch and the Inquistion released them for being deluded.
If we'er talking about the "Witch Hunts" it is important to understand that these had nothing to do with Paganism or with witchcraft as we know it today. Most of the victims of these Witch Hunts were simply people who weren't much liked in their community. What better way to get rid of someone you didn't like and take their property than by saying they were a Witch. Most of the people killed were good Christians who feel afoul of their neighbors. No one was hunted down because of their Pagan religion.