This is a randomized (study drug assigned by chance), double-blind (neither the Investigator nor the participant know the treatment) placebo-controlled and multicenter (when more than 1 hospital or medical school team work on a medical research study) study to determine if participants with chemotherapy-naive mCRPC will benefit from the addition of apalutamide to AAP compared with AAP alone. The study consists of 3 phases: Screening phase; Treatment phase, and Follow-up phase. Participants' safety will be monitored throughout the study.