Study of REGN13335 in Adult Participants With Pulmonary Arterial Hypertension (PAH)

Key Inclusion Criteria: 1. Documented clinical diagnosis of PAH (Group 1 PH according to the 7th World Symposium on Pulmonary Hypertension (WSPH)) 2. WHO functional class II or III (slight to marked limitation of functional status due to PAH) 3. Receiving background Standard Of Care (SOC) therapy for PAH on a stable dose and regimen, as determined by the investigator, as described in the protocol 4. PVR ≥400 dynes∙sec/cm\^5 (5 Wood units) based on Right Heart Catheterization (RHC) during the screening period 5. Has 6MWD ≥150 and ≤550 meters repeated twice during screening as described in the protocol Key Exclusion Criteria: 1. Has Group 2 (PH associated with left heart disease), Group 3 (PH associated with lung diseases and/or hypoxia), Group 4 (PH associated with pulmonary artery obstructions), or Group 5 (PH with unclear and/or multifactorial mechanisms) PH according to the 7th WSPH 2. Pulmonary Arterial Wedge Pressure (PAWP) \>15 mm Hg by RHC during the screening period 3. History of left-sided heart disease and/or clinically significant cardiac disease, as described in the protocol 4. Obstructive lung disease defined as Forced Expiratory Volume in 1 second (FEV1)/Forced Vital Capacity \<0.7 and FEV1 \<70% of the predicted value as described in the protocol 5. Evidence of interstitial lung disease as defined in the protocol 6. Evidence of chronic thromboembolic pulmonary disease or acute pulmonary embolism as described in the protocol 7. Participants requiring anticoagulation and/or antiplatelet therapy for an underlying medical condition as described in the protocol 8. Has any history of intracranial bleeding or any history of elevated intracranial pressure 9. Has any history of bleeding meeting criteria as described in the protocol Note: Other protocol-defined Inclusion/ Exclusion criteria apply