Clinical Study to Compare the Efficacy and Safety of Macitentan and Tadalafil Monotherapies With the Corresponding Fixed-dose Combination Therapy in Subjects With Pulmonary Arterial Hypertension (PAH)

Inclusion Criteria: * Signed and dated informed consent form (ICF) * Confirmed diagnosis of symptomatic PAH in WHO FC II or III * Symptomatic PAH belonging to one of the following subgroups of WHO Group 1 pulmonary hypertension: * Idiopathic * Heritable * Drug- or toxin-induced * Associated with connective tissue disease, HIV infection, portal hypertension or congenital heart disease with simple systemic-to-pulmonary shunt with persistent pulmonary hypertension documented by a right heart catheterization (RHC) ≥ 1 year after surgical repair * PAH diagnosis confirmed by hemodynamic evaluation at rest (through central reading), evaluated within 5 weeks prior to randomization: * Mean pulmonary artery pressure (mPAP) ≥ 25 mmHg, AND * Pulmonary artery wedge pressure (PAWP) or left ventricular end diastolic pressure (LVEDP) ≤ 15 mmHg, AND * Pulmonary vascular resistance (PVR) ≥ 3 WU (i.e., ≥ 240 dyn∙sec∙cm-5) * Negative vasoreactivity test in idiopathic, heritable, and drug/toxin-induced PAH. (Participants for whom no vasoreactivity test was performed at diagnosis can be eligible if currently treated with PAH therapy for more than 3 months and PAH diagnosis confirmed by hemodynamic evaluation at least 3 months after introduction of their PAH therapy). * Currently receiving a stable dose of ERA or PDE-5i monotherapy for at least 3 months prior to baseline RHC, within the prespecified doses in the study protocol or no history of PAH-specific treatment * Participant a…