A Two-Part Multicenter, Double-Blind, Randomized Placebo-Controlled Study to Evaluate Efficacy and Safety and the Maintenance of Effect of 20-(Milligram) mg Seltorexant as Adjunctive Therapy to Antidepressants in Adult and Elderly Patients With Major Depressive Disorder With Insomnia Symptoms

Inclusion Criteria: Participants in part 1 and direct enrollers to part 2: * Meet DSM-5 MDD, without psychotic features based upon clinical assessment and confirmed by the structured clinical interview for DSM-5 Axis I disorders-clinical trials version (SCID-CT) diagnosed with first depressive episode prior to age 60 * Have had an inadequate response to at least 1 but no more than 2 antidepressants, administered at an adequate dose and duration in the current episode of depression. An inadequate response is defined as less than (\<) 50% reduction but with some improvement (that is, improveme…