This clinical trial is focused on studying Pulmonary Arterial Hypertension (PAH), a condition characterized by high blood pressure in the arteries of the lungs. The study will evaluate the effectiveness and safety of a treatment called seralutinib, which is administered as an inhalation powder in a hard capsule. Participants will either receive seralutinib or a placebo, which looks identical to the treatment but does not contain the active substance.

The purpose of the study is to assess how seralutinib affects exercise capacity after 24 weeks of treatment when used alongside existing PAH medications. Participants will be randomly assigned to receive either seralutinib or the placebo, and neither the participants nor the researchers will know who is receiving which treatment. The study will last for a total of 48 weeks, during which participants will continue their regular PAH treatment while adding the study medication or placebo.

Throughout the study, participants will undergo various assessments to monitor their health and the effects of the treatment. These assessments will include measuring the distance they can walk in six minutes, which helps evaluate their exercise capacity. The study aims to provide valuable information on whether seralutinib can improve the quality of life for individuals with PAH by enhancing their ability to exercise and perform daily activities.