How to handle the situation, if the Secretary is asked to perform a function which is usually handled by an officer of a higher level?

If a secretary succeeds to accomplish that task carefully, in future he might be assigned the more similar duties and he might be included in the higher level officers by getting promotion according to his abilities.

Observation and knowledge will play an important role here, everyone observe everthing, a secratery must have observed what was the officer doing, obviously observing will lead to gain the knowledge. and this is how the situation can be handled

Make it successful, you are lucky if you are given the privilege.