Forgive me if this has been asked. I did try searching, and I am not even sure of the correct search terms!

I have two free night certificates with Hilton. I plan to book a five night stay in Anchorage this summer. I have enough points, but I'd prefer to not use so many as I'm not points "rich." My question is this:
If I use one (or both, but one expires this summer) of those free night certificates for one of the four nights, do I then pay for three (or two, if I use both) more standard nights on points and get five, or does a certificate night not count as a points night and just have its own category, so it's best not to use it with a four night stay?

I apologize if I didn't even ask that clearly!