Since its release in 2005, the second edition of WFRP has accumulated a large body of official and third-party material, and a large, active, and loyal community.
Since the 4th edition's release in December 2018, it has steadily grown in popularity, and players and GMs now have about six months of experience with the rules. 4th edition material is being released, but there are 14 years of well-played material — settings, careers, adventures, etc — already out there.
The 4th edition rules are quite close to 2nd edition, but there are some important differences when trying to adapt 2nd edition materials and adventures for use with the new rules. So:
What are the major differences that GMs and players need to be attentive to when moving to WFRP 4e? What changes are likely be needed to bring 2e careers or adventures into a 4e campaign?