Is it wrong to celebrate Christmas? Is it pagan?

Good, succinct explanation from Steve Hays:
http://triablogue.blogspot.com/2016/12/is-it-wrong-for-christians-to-celebrate.html

It's all about a robust view of God's creation. It's God's creation.
Others might *claim* that this or that day/place/thing/etc. now belongs
to Moloch. So what? All kinds of claims are made by all kinds of people.
But mere hot air doesn't change reality. At the end of it all,
everything still belongs to God.