If it is from WWII, it would be over 50 years old and therefore considered a "Curios and Relics" firearm. However depending on the rifle, it may be considered a NFA firearm, meaning the executor would have to submit paperwork to the ATF and the recipient would have to go through a background check.
If you post photos of the rifle, especially any and all markings, we should be able to identify the rifle and determine your next step.
EDIT: What ET said is true, however there are a few rifles are very collectible and worth a lot of money, such as, a Japanese rifle with the Emperor's mark intact.