I already paid the postal fees
If you have already paid the postal fee, you will receive a .pdf containing your customs declaration to print your declaration at home, as well as a withdrawal code (valid for 10 days) to print it at the post office.
I did not paid the postal fees
If you have not paid the postal fees, you will only receive a withdrawal code (valid for 10 days) to present at the post office to print your customs declaration.