"Is it necessary to buy it?"
Translation:E necesar să îl cumpăr?
A literal translation of the Romanian sentence would be:
"Is it necessary that I buy it!"
But we don't talk like that in English. We'd usually use a personal structure "Do I need to buy it", but if we use the impersonal construction with "it", then we use the infinitive, as in DL's sentence. Who it refers to would be clear from the context.