This trial is testing sotatercept, a new medication, to see if it can help people with a specific type of high blood pressure in the lungs (PAH) when added to their usual treatment. The study focuses on patients who are newly diagnosed and at higher risk of their condition worsening. Sotatercept aims to reduce the pressure in the lung's blood vessels, potentially slowing down disease progression. Sotatercept has shown significant reduction in pulmonary vascular resistance and maintained clinical efficacy in previous studies.