Inclusion Criteria:

          -  Male participants with histologically- or cytologically-confirmed adenocarcinoma of
             the prostate without small cell histology

          -  Has metastatic disease assessed by investigator and verified by BICR by either ≥2 bone
             lesions on bone scan and/or visceral disease by computed tomography/magnetic resonance
             imaging (CT/MRI)

          -  Willing to maintain continuous ADT with a LHRH agonists or antagonists during study
             treatment or have a history of bilateral orchiectomy

          -  Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 assessed
             within 10 days of randomization

          -  Participants receiving bone resorptive therapy (including, but not limited to,
             bisphosphonate or denosumab) must have been on stable doses prior to randomization

          -  Has adequate organ function

          -  Has provided newly obtained core or excisional biopsy (obtained within 12 months of
             screening) from soft tissue not previously irradiated (samples from tumors progressing
             in a prior site of radiation are allowed). Participants with bone only or bone
             predominant disease may provide a bone biopsy sample

          -  Male participants must agree to the following during the intervention period and for
             at least 120 days after the last dose of study intervention: Refrain from donating
             sperm PLUS either be abstinent from heterosexual intercourse and agree to remain
             abstinent OR agree to use contraception, unless confirmed to be azoospermic

          -  Male participants must agree to use male condom when engaging in any activity that
             allows for passage of ejaculate to another person of any sex

        Exclusion Criteria:

          -  Has a known additional malignancy that is progressing or has required active treatment
             in the last 3 years

          -  Has an active autoimmune disease that has required systemic treatment in past 2 years

          -  Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy

          -  Has undergone major surgery including local prostate intervention (excluding prostate
             biopsy) within 28 days prior to randomization and not recovered adequately from the
             toxicities and/or complications

          -  Has a gastrointestinal disorder affecting absorption or is unable to swallow
             tablets/capsules

          -  Has an active infection (including tuberculosis) requiring systemic therapy

          -  Has a history of (non-infectious) pneumonitis that required steroids or has current
             pneumonitis

          -  Has known active human immunodeficiency virus (HIV), hepatitis B virus (HBV) or
             hepatitis C virus (HCV) infection

          -  Has known or suspected central nervous system (CNS) metastases and/or carcinomatous
             meningitis

          -  Has a history of seizure or any condition that may predispose to seizure

          -  Has a history of loss of consciousness within 12 months of screening

          -  Has had myocardial infarction or uncontrolled angina within 6 months prior to
             randomization, or has New York Heart Association class III or IV congestive heart
             failure or a history of New York Heart Association class III or IV congestive heart
             failure

          -  Has hypotension (systolic blood pressure <86 millimeters of mercury [mmHg]) or
             uncontrolled hypertension (systolic blood pressure >170 mmHg or diastolic blood
             pressure >105 mmHg) at the screening visit

          -  Has a history of clinically significant ventricular arrhythmias

          -  Has hypersensitivity to pembrolizumab and/or enzalutamide and/or any of their
             excipients

          -  Has received prior ADT as neoadjuvant/adjuvant therapy for non-metastatic prostate
             cancer for >39 months in duration or within 9 months prior to randomization or with
             evidence of disease progression while receiving ADT

          -  Has had prior treatment with a next generation hormonal agent (eg, abiraterone,
             enzalutamide, apalutamide, darolutamide)

          -  Has received prior therapy with an anti-programmed cell death-1 (anti-PD-1),
             anti-programmed cell death-ligand 1 (anti-PD-L1), or anti PD-L2 agent or with an agent
             directed to another stimulatory or coinhibitory T-cell receptor

          -  Has received a live vaccine within 30 days prior to randomization

          -  Has a "superscan" bone scan

          -  Has had an allogenic tissue/solid organ transplant

          -  Is expecting to conceive or father children within the projected duration of the
             study, starting with the screening visit through 120 days after the last dose of study
             treatment

          -  Has received any prior pharmacotherapy, radiation therapy or surgery for metastatic
             prostate cancer with the following exceptions:

               1. Up to 3 months of ADT or orchiectomy with or without concurrent first-generation
                  antiandrogens, if patient was not treated with docetaxel

               2. May have 1 course of palliative radiation or surgical therapy to treat symptoms
                  resulting from metastatic disease if it was administered at least 4 weeks prior
                  to randomization

               3. For participants with low volume metastatic disease, may have 1 course of
                  definitive radiotherapy if it was administered at least 4 weeks prior to
                  randomization

               4. Up to 6 cycles of docetaxel therapy with final treatment administration completed
                  within 2 months of randomization and no evidence of disease progression. In these
                  participants up to 6 months of ADT permitted