greetings,

the case of each entrance examination is different.

In some, the invigilator keeps the admit card but in most of the cases of prominant entrances, the admit card is signed by the invigilator and is duely returned to the candidate.

the admit card is a very important document and must be kept safely untill the admission process is complete i.e councelling process has been attended and seat has been reserved.

it acts as a proof of the candidate's presence during the entrance examination.

hope this helps.

good luck!