A Study of JNJ-64042056 in Participants With Preclinical Alzheimer's Disease

The purpose of this study is to assess whether JNJ-64042056 affects the spread and build up of tau (a protein in brain) when compared with placebo, using brain scan (tau PET) to determine results from specific areas of the brain.

Inclusion Criteria: * Elevated brain tau pathology defined as Braak 3 region of interest standardized uptake value ratio (ROI SUVR) greater than (\>) 1.1 (or equivalent based on emerging data) on a screening tau PET scan, reviewed centrally by a qualified reader to enrich for probability of disease progression during the study * Clinical Dementia Rating (CDR) global score of 0 at screening and baseline * Mini Mental State Examination (MMSE) greater than or equal to (\>=) 27 (with educational adjustment) at screening * Able to read and write and with a minimum 5 years of formal education as reported by participant and study partner at screening * A participant must be of non-childbearing potential Exclusion Criteria: * History consistent with or known autosomal dominant AD (mutation identified in the family and/or participant) * Fulfills diagnostic criteria for Alzheimer's Dementia or non-Alzheimer's Dementia, including, but not limited to Frontotemporal Dementia (FTD), Diffuse Lewy Body Dementia (DLBD), Vascular Dementia (VAD), alcoholic dementia, Parkinson's dementia, Korsakov, Creutzfeldt-Jakob or other prion diseases, Posterior Cortical Atrophy * Diagnosis of Mild Cognitive Impairment (MCI) * Vitamin B12 or folate levels below the central laboratory lower limit of normal, unless the investigator determines that supplementation is not required after randomization * History of or current neurological disease other than preclinical AD that may make interpretation of possible new neurological signs or symptoms difficult