Pamporovo is a popular resort in Europe. Therefore, answering the question "how to get to Pamporovo" is very easy. There are direct buses from Sofia's central bus station. You will be on the road for four hours, and a ticket will cost you 20 BGN. You can check the bus schedule at Sofia Central Bus Station.
Sofia itself can be reached from the airport by buses #84 (Terminal 1) and #384 for 2 BGN or a shuttle for 1.5 BGN.
You can also rent a car and go to Pamporovo on your own. Some hotels provide their guests with a direct transfer from the airport. However, you should inquire about this option in advance when booking a reservation at the hotel.