You are required to have a valid visa to enter Bhutan. The Bhutanese Embassies abroad do not issue visa 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 at 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 passport that is valid for at least six months beyond the length of stay.
The Visa fee is US$40, and Tourism Development Fund (TDF) is US$10 these fees need to be sent together with the tour payment.