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: * Adult participants ≥ 18 years of age * Symptomatic World Health Organization (WHO) Group 1 Pulmonary Hypertension (PH)(PAH) classified by one of the following subgroups: * Idiopathic pulmonary arterial hypertension (IPAH); * Heritable pulmonary arterial hypertension (HPAH); * Associated with drugs and toxins; * PAH associated with: * Connective tissue disease * Congenital systemic-pulmonary intracardiac shunt * Has the following hemodynamic parameters that are consistent with the diagnosis of PAH: * Mean pulmonary arterial pressure (mPAP) \> 20 mmHg at rest, AND * Pulmonary artery wedge pressure (PAWP) ≤ 15 mmHg, AND * PVR ≥ 5 Wood Units (400 dyn·sec·cm-5) * Has WHO/New York Heart Association (NYHA) Functional Class (FC) II or III symptoms as assessed by the Investigator * 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) * 6MWD ≥ 150 and ≤ 500 meters at screening * Provide written (signed and dated) informed consent form before the initiation of any Screening tests or procedures Exclusion Criteria: * Evidence or history of left ventricular dysfunction and/or clinically significant cardiac disease * Has pulmonary function tests (PFTs) with evidence of significant obstructive or parenchymal lung disease * 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 * Has uncontrolled systemic hypertension * Hemoglobin \< 9 g/dL at Screening * Prior heart or heart-lung transplants, active on the lung transplant list, or life expectancy of \< 12 months per Investigator assessment * Diagnosis of pulmonary veno-occlusive disease or pulmonary capillary hemangiomatosis * Initiation or discontinuation of an exercise program for cardiopulmonary rehabilitation within 90 days prior to Baseline or planned initiation during the study * Prior participation in a KER-012 study or prior treatment with a therapy targeting TGF-β superfamily (e.g. sotatercept) * Prior participation in another interventional clinical study with medicinal products within 30 days or 5 half-lives prior to Screening, whichever is longer