Inclusion Criteria:  History of PAH belonging to one of the following subgroups of the Clinical Classification Group 1 (WHO):  participants with idiopathic pulmonary arterial hypertension (IPAH) Hereditary pulmonary arterial hypertension Congenital heart disease (surgically repaired at least 12 months prior to screening) drug or toxin induced (for example, anorexigen, or methamphetamine use). Resting mean pulmonary arterial pressure (mPAP) > 25 mmHg; pulmonary capillary wedge pressure (PCWP) or left ventricular end diastolic pressure < 15 mmHg, as determined by right heart catheterization within 20 days of randomization. Pulmonary Vascular Resistance > 6 Wood units (480 dynes s/cm-5), as determined by right heart catheterization within 20 days of randomization. WHO Functional Class II-III  6MWD must be between 150 and 550 m (inclusive). The qualifying test needs to be within 20 days of randomization. To meet the above criterion additional six minute walk test (6MWT) may be performed up to a maximum of 3 tests in total prior to dosing; the minimal time difference between two tests should be at least 4 h.  Standard of care therapy which is stable at least 6 weeks prior to RHC and qualifying 6MWT assessment within 20 days of randomization. Standard of care includes one or more of the following treatments: prostacyclin analogues and receptor agonists (if I.V., dose adjustments must be within 20% of initial stable dose) endothelin receptor antagonists (ERAs) phosphodiesterase type 5 inhibitors (PDE5i) soluble guanylate cyclase (sGC) stimulators  Exclusion Criteria:  Participants with pulmonary hypertension (PH) in the Clinical Classification Groups 2-5 (WHO), and any PAH Group 1 subgroups not covered by Inclusion Criterion #4. Participants with a history of left sided heart disease, chronic left sided heart failure, congenital or acquired valvular disease compromising left ventricular function and/or pulmonary venous hypertension or symptomatic coronary disease (non-symptomatic, revascularized coronary artery disease would be acceptable). Participants with obstructive lung disease defined as: FEV1/FVC < 60% and FEV1 < 60% of predicted value after bronchodilator administration as well as participants with moderate or severe restrictive lung disease: Total Lung Capacity < 70% of predicted value. Testing must have occurred within 24months of screening. If historical testing is not available, then lung function testing must be conducted during the screening period. Acute or chronic impairment (other than dyspnea), which would limit the ability to comply with study requirements, including interference with physical activity and execution of study procedures such as 6MWT (e.g., angina pectoris, claudication, musculoskeletal disorder, multiple sclerosis, need for walking aids).  Additional protocol-defined inclusion / exclusion criteria may apply.