• Clarified that when a Study Drug Termination Visit occurred close in time to the next regular visit, the Study Drug Termination Visit could take the place of the next regularly scheduled visit. • Clarified CPET procedures and variables and the scope of the CPET core laboratory. • Added details around the full physical examination. • Removed echocardiogram as a required assessment. • Added CD4+ test to list of laboratory tests. • Added language to ensure subjects were not excluded due to a positive drug screen caused by prescription medication. • Changed timeframe of diagnostic right heart catheterization from 1 to 3 years before Screening. • Removed time restriction of ventilation-perfusion lung scan. • Updated number of centers to “50 to 60”. • Updated inclusion criterion for stable dose(s) of PAH-specific oral therapy to be defined as no change in dose or regimen for at least 120 days prior to Randomization. • Added that eligible male subjects must agree not to participate in sperm donation for 90 days after the last dose of study drug, and changed the timeframe for the prohibition on conception from 28 to 30 days. • Removed current unstable angina as an exclusion criterion. • Updated chronic renal insufficiency to be defined using estimated glomerular filtration rate using the Modification of Diet in Renal Disease Study equation instead of creatinine. • Updated exclusion criterion timeframe for diagnosed and/or treated malignancy from within 5 to 3 years of Screening. • Added clarification around how to deal with contact between scheduled clinic visits (timing of calls, what to do after Week 16, etc). • Added description that the Investigator would attempt to discuss unblinding with the Sponsor prior to unblinding. • Removed electrocardiogram response to exercise and duration of exercise from additional endpoints.

• Aligned definition of PAH and risk categories with current European Society of Cardiology/European Respiratory Society guidelines. • Changed pulmonary vascular resistance requirement from ≥3 (240 dynes/sec/cm5) to >2 (160 dynes/sec/cm5) Wood units. • Clarified that the study would end when all subjects completed their final study visit. • Clarified that subjects did not need to have newly initiated therapy to be eligible. • Added that subjects must have completed ROR-PH-302 on study drug to be eligible for the OLE study. • Removed limitation of only 1 re-test for re-screened subjects. • Clarified that subjects who discontinued study drug after Week 24 would attend the Follow-up Visit. • Removed specifics for biological quality control test timing from protocol. • Clarified that only 1 CPET was required prior to randomization. • Clarified that electrocardiograms were recorded in triplicate using a device provided by the Sponsor unless not allowed by local regulations. • Clarified AE collection procedures. Updated nonserious AE monitoring procedures. • Revised urine human chorionic gonadotropin analysis for females of childbearing potential instead of only postmenopausal females. • Revised the requirement for stable doses of PAH-specific oral therapy prior to randomization from 120 days to 90 days. • Removed VE/VCO2 slope requirement for study entry. • Amended required peak VO2 from ≥10 to ≥9 mL/min/kg (upper limit remained <18 mL/min/kg). • Removed requirement for dosage of concomitant medications to remain unchanged throughout the study. • Updated exclusion criteria to allow prostacyclin pathway agents for PAH within 90 days of randomization. • Clarified that PAH-specific medications are not to be added or changed during the study. • Added that if study was terminated early for safety reasons, the Sponsor would inform regulatory authorities without delay in accordance with local reporting requirements.