A Study to Investigate the Safety and Efficacy of KER-012 in Combination With Background Therapy in Adult Participants With Pulmonary Arterial Hypertension (PAH) (TROPOS Study).

Inclusion Criteria:

1. Adult participants ≥ 18 years of age
2. Symptomatic World Health Organization (WHO) Group 1 Pulmonary Hypertension (PH)(PAH) classified by one of the following subgroups:

1. Idiopathic pulmonary arterial hypertension (IPAH);
2. Heritable pulmonary arterial hypertension (HPAH);
3. Associated with drugs and toxins;
4. PAH associated with:

1. Connective tissue disease
2. Congenital systemic-pulmonary intracardiac shunt
3. Has the following hemodynamic parameters that are consistent with the diagnosis of PAH:

1. Mean pulmonary arterial pressure (mPAP) > 20 mmHg at rest, AND
2. Pulmonary artery wedge pressure (PAWP) ≤ 15 mmHg, AND
3. PVR ≥ 5 Wood Units (400 dyn·sec·cm-5)
4. Has WHO/New York Heart Association (NYHA) Functional Class (FC) II or III symptoms as assessed by the Investigator
5. Must be on a stable PAH background therapy with either an endothelin-receptor antagonist (ERA) and/or a phosphodiesterase-5 inhibitor (PDE5-I) or soluble guanylate cyclase (sGC) stimulator and/or prostacyclin analogue or receptor agonist (oral/inhaled/SC/intravenous)
6. 6MWD ≥ 150 and ≤ 500 meters at screening
7. Provide written (signed and dated) informed consent form before the initiation of any Screening tests or procedures

Exclusion Criteria:

1. Evidence or history of left ventricular dysfunction and/or clinically significant cardiac disease
2. Has pulmonary function tests (PFTs) with evidence of significant obstructive or parenchymal lung disease
3. Evidence of thromboembolic disease assessed by ventilation perfusion (V/Q) lung scan or other local standard of care diagnostic evaluation at the time of PAH diagnosis or after
4. Has uncontrolled systemic hypertension
5. Hemoglobin < 9 g/dL at Screening
6. Prior heart or heart-lung transplants, active on the lung transplant list, or life expectancy of < 12 months per Investigator assessment
7. Diagnosis of pulmonary veno-occlusive disease or pulmonary capillary hemangiomatosis
8. Initiation or discontinuation of an exercise program for cardiopulmonary rehabilitation within 90 days prior to Baseline or planned initiation during the study
9. Prior participation in a KER-012 study or prior treatment with a therapy targeting TGF-β superfamily (e.g. sotatercept)
10. Prior participation in another interventional clinical study with medicinal products within 30 days or 5 half-lives prior to Screening, whichever is longer