The study is looking at how well a drug called **ralinepag** works and how safe it is for people with Pulmonary Arterial Hypertension (**PAH**). PAH is a serious condition where the blood vessels in the lungs become narrow, causing high blood pressure. The study will compare ralinepag to a placebo, which is a pill that looks like the real drug but has no medicine. People who join will be randomly assigned to take either ralinepag or the placebo, along with their regular PAH treatment.

**Key Points:**

• The study lasts until the target number of events is reached, with an option to continue in an extension study.
• Participants must visit the study site regularly for check-ups and tests.
• People in the study will not know if they are receiving ralinepag or the placebo.

Eligible participants need to be 18 or older, have PAH, and be stable on their current PAH medications. People cannot join if they have other significant health issues like severe liver disease or recent cancer. Participants must also agree to use effective birth control during the study.