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 28 BGN. You can check the bus schedule at Sofia Central Bus Station.
You can reach Sofia from the airport by buses № 84 (Terminal 1) and № 384 for 2 BGN, or by shuttle for 1.5 BGN.
You can also rent a car and travel to Pamporovo on your own. Some hotels offer direct airport transfers for their guests, but you should inquire about this option in advance when booking your stay.