popuniti

1. (of a form) to fill in; to fill out
   Popunio sam prijavu i predao je na šalteru. — I filled out the application and handed it in at the counter.
   Molim vas, popunite ovaj formular. — Please fill in this form.
2. to fill
   Firma je brzo popunila slobodno radno mesto. — The company quickly filled the vacancy.
   Sva mesta u sali su popunjena. — All the seats in the hall are taken.
3. colloq. (popuniti se) to fill out; to put on weight
   Popunila se malo otkako je prestala da puši. — She's filled out a bit since she quit smoking.

The imperfective counterpart is popunjavati.