What does it mean in other words?
prior to the offering

THE CONTEXT:

As part of formality and prior to the offering, we would require a reference check for his file and Martina has kindly provided you as her referee.

Question

What does it mean in other words?
prior to the offering

THE CONTEXT:

As part of formality and prior to the offering, we would require a reference check for his file and Martina  has kindly provided you as her referee.

Answer

'prior to the offering' means that something is needed before a deal can be reached or agreed.  In this case the reference check must be given by Martina before anything can be offered.