You are required to have a valid visa to enter Bhutan. The Bhutanese Embassies abroad do not issue visas, and visa on arrival is non-existent. It is to get the visa for Bhutan before arriving.
You are required to submit a scanned copy of your passport details four weeks in advance before your arrival date. Your travel company will process your application and provide you with a copy of the Visa. It usually takes 2-3 working days for the application to be approved.
You need to have a valid passport for at least six months beyond the length of stay.
The Visa fee is US$40, and the Tourism Development Fund (TDF) is US$10. These fees need to be sent together with the tour payment.