But this is not your problem. Your pointers are compatibles, so your code is OK.
The error error C2446: ==': no hay conversi?n de ‘ACharacter *’ en ‘AActor *’ and others of the same type are frequent since 4.15.
You need to add
#include “GameFramework/Character.h”
to your Pickup.ccp list of #include.
The reason: ACharacter is now simply referenced by class ACharacter; a forward declaration, the compiler cannot know it’s an AActor derived class until you declare the “real” class (with the proper #include)