RecruitingPhase 2Biological interventionA Study of Sotatercept (MK-7962) in Japanese Children With Pulmonary Arterial Hypertension (PAH) (MK-7962-032)The goal of this study is to learn about the safety of sotatercept and how well Japanese children tolerate it, when taken along with standard (usual) pulmonary arterial hypertension (PAH) treatment. Researchers also want to learn what happens to it in a person's body over time and whether it lowers resistance in blood vessels in the lungs.