I just got the BRTA licence extract a few days ago. You'll have to make two copies of your original driving licence, make an application addressed to the assistant director of BRTA for a certificate (that's the extract) and for an attested copy of your licence. You'll need to pay BDT 137 (from what i remember) in the Brac bank counter # 15 at BRTA payment booth. With the application, copies of original licence, and money receipt you'll have to go to Room number 112 of BRTA, submit those. They'll check with their record whether your licence is original or not and then will receive it. They'll give you a delivery date, around 7 days.
The letter is very normal, written in their letterhead pad, confirming that your licence is original, first date of issue, DOB and your full name. It will be signed by the Assistant Director of BRTA. Along with the letter they'll give you your copy of original licence back, attested by the same person.
Hope it helps.
