The purpose of this study is to learn about the long-term safety, tolerability and effects of the study medicine (PF-07868489) for the possible treatment of PAH. PAH is a condition in which there is high blood pressure in the arteries that carry blood from the heart to the lungs. This high pressure makes it harder for the heart to pump blood through those lungs, potentially damaging the right side of the heart. This is an open-label study. Which means that both the healthcare providers and the study participants are aware of the medicine being given. This study is also an extension study with study medicine (PF-07868489). An extension study allows patients from an earlier clinical study (also called as qualifying study) to continue participating to assess long-term benefits and safety of the medicine.