While the question literally does ask for a "recommendation", this is really a Resource Request question: it is asking for a resource which gives a detailed explanation of a particular topic. The topic is specific: the declarations, laws, and statements of popes. The scope is narrow: during the time of the Protestant Reformation. And most importantly, it does not fall into the problem area that most recommendations fall into: opinion. It doesn't ask for evaluation of these popes' statements, criticism of the Reformation or the Counter-Reformation, etc. What sort of opinions do you think the question will invite? Which resource is the most detailed? If someone thinks there is a resource that is more detailed than the one from Geremia's answer, well that may technically be their opinion, but I think most of us would be happy to see an answer revealing this better resource to us. The opinions people could have about this subject matter aren't like the opinions of the banned recommendation questions across the network (what's your favourite band? Which book series should I read next? Things like that.)
As it is neither open ended nor inviting of (problematic) opinions, I voted to keep the question open when I went through the close vote review queue earlier today. I assume your flag was automatically handled via the review queue. Other site members may disagree, and if the community does decide to close it, that's perfectly fine.