A Study of ROC-101 in Patients With Pulmonary Arterial Hypertension (PAH) and Pulmonary Hypertension Associated With Interstitial Lung Disease (ILD-PH) (ROCSTAR STUDY)

Key Inclusion Criteria: 1. Must be age 18 or older at the time of signing the informed consent form (ICF). The participant must understand and voluntarily sign an ICF prior to any study-related procedures 2. Documented findings on a right heart catheterization (RHC) consistent with a diagnosis World Health Organization (WHO) Group 1 PAH or WHO GROUP 3 PAH 3. Symptomatic Pulmonary Hypertension (PH) classified as WHO Functional Class II or III symptoms 4. PAH participants: Pulmonary Vascular Resistance (PVR) of ≥ 5 Wood units (≥ 400 dynes/sec/cm-5) and, Pulmonary Capillary Wedge Pressure (PCWP) ≤ 15 mmHg and Mean Pulmonary Arterial Pressure (mPAP) \> 20 mm Hg and ILD-PH participants: PVR of ≥ 3 Wood units (≥ 240 dynes/sec/cm-5) with a maximum enrollment of 5 participants with PVR between 3 and 4 Wood units inclusive (240-320 dynes/sec/cm-5 inclusive) and the remaining 5 participants must have PVR \>4 Wood units (\> 320 dynes/sec/cm-5) and, PCWP ≤ 15 mmHg and mPAP \> 20 mm Hg 5. Participants on stable background therapy for PAH or ILD-PH. 6. Females of childbearing potential (as defined in protocol) must agree to use highly effective contraception (as defined in the protocol) 7. Male participants must follow protocol-specified contraception guidance. 8. Participants must be able to communicate well with Investigators, understand the study procedures in the ICF and are agreeable to complete the study in accordance with the protocol. 9. Must be able to swallow tablets. 10. Pulmonary function tests (PFT): PAH participants at Screening as follows: 1. Forced Vital Capacity (FVC) \> 70% predicted; or if between 60% to 70% predicted, or if not possible to be determined, confirmatory High-Resolution Computed Tomography (HRCT) indicating no more than mild (\<10% fibrosis) ILD and emphysema (less than 10%); and 2. The ratio of FEV1 (first second)/FVC \> 0.70 of predicted. ILD-PH participants at Screening as follows: 1. PFTs consistent with their ILD diagnosis and showing FEV1/ FVC ratio \> 65% and HRCT having more than 10% fibrosis and less than 10% emphysema, based on the proportion of lung parenchyma affected by fibrotic and emphysema changes. and, 2. Minimum FVC of 50% and diffusing capacity for carbon monoxide (DLCO) (corrected for Hb g/dl) \>25% 11. In PAH participants, i.e., Cohorts 1 and 2 only, ventilation-perfusion (VQ) scan (or, if unavailable, a negative Computed tomography pulmonary angiogram \[CTPA\] or pulmonary angiography result), any time prior to Screening or conducted during the Screening Period, with a normal or low probability result that is not clinically significant 12. Acceptable Electrocardiogram (ECG) findings as assessed by the Investigator or qualified designee at the Screening Visit and at the Baseline Visit (Day 1), including each criterion as listed below: * Normal sinus rhythm (HR) between 40 and 100 beats per minute, inclusive); * Corrected QT Interval (QTcF) interval ≤ 450 msec (males) and ≤ 460 msec (females); * QRS interval ≤ 120 msec; if \> 120 msec, result will be confirmed by a manual overread 13. Body weight at the Screening visit and at Baseline (Day 1) is greater than 50.0 kg and the body mass index (BMI) is in the range of 19.00 to 36.00 kg/m2, inclusive 14. 6MWD ≥ 100 and ≤ 550 meters repeated twice, once during Screening Period and once at the Baseline Visit (Day 1) and both values within 15% of each other, allowing for a third repeat if \> 15% difference, calculated from the higher/highest value Key Exclusion Criteria: 1. Diagnosis of PH WHO Groups 2, 4, or 5 2. Diagnosis of the following PAH Group 1 subtypes: human immunodeficiency virus (HIV)-associated PAH, PAH associated with portal hypertension, schistosomiasis-associated PAH and pulmonary veno-occlusive disease and/or pulmonary capillary hemangiomatosis 3. Positive blood test for hepatitis B virus surface antigen (HBsAg), hepatitis C virus (HCV) antibody (HCVAb) (unless participants have had treatment for HCV and have a negative HCV ribonucleic acid \[RNA\] polymerase chain reaction \[PCR\]) or HIV antibody 4. Participants with known hypersensitivity to ROC-101 or any components of its formulations 5. History of malignancy within the last 5 years, with the exception of fully excised or treated basal cell carcinoma, cervical carcinoma in-situ, or ≤ 2 squamous cell carcinomas of the skin 6. History of clinically significant (as determined by the Investigator) non-PAH related cardiac, endocrine, hematologic, hepatic, immune, metabolic, urologic, pulmonary, neurologic, neuromuscular, dermatologic, psychiatric, renal, and/or other diseases that may limit participation in the study 7. Participation in another clinical trial involving intervention with another investigational drug, approved therapy for investigational use, or investigational device within 4 weeks prior to Baseline Visit (unless it is in the follow-up period of an interventional study), or if the half-life of the previous product is known, within 5× the half-life prior to Baseline Visit (Day 1), whichever is longer 8. Major surgery within 8 weeks prior to Baseline Visit (Day 1) or major surgery scheduled or planned in the main study. Participants must have completely recovered from any previous surgery prior to the Screening Visit 9. Prior heart or heart-lung transplants, or a participant listed for heart and/or lung transplantation or prior pneumonectomy 10. Pregnant or breastfeeding females 11. Males who do not agree to protocol contraception guidelines 12. Uncontrolled systemic hypertension as evidenced by sitting SBP \> 160 mm Hg or sitting diastolic BP \> 100 mm Hg during Screening Visit and Baseline Visit (Day 1) after a period of rest 13. Systolic BP \< 90 mm Hg during Screening Visit or at Baseline Visit (Day 1) or, if during screening, orthostatic systolic BP decreases by more than 20 mm Hg and the participant is symptomatic. 14. History of known pericardial constriction or a clinically significant (more than trace or trivial \[i.e., ≥10 mm\]) pericardial effusion seen in diastole or in both systole and diastole on echocardiogram (ECHO) historically and confirmed on screening ECHO 15. RHC contraindicated during the study per Investigator 16. Cerebrovascular accident within 3 months (120 days) of start of Screening 17. History of restrictive or constrictive or congestive cardiomyopathy 18. Left ventricular ejection fraction (LVEF) \< 50% on historical echocardiogram (ECHO) performed within 6 months prior to start of Screening period (and confirmed during the Screening ECHO) or grade 2 or higher diastolic dysfunction 19. Any current symptomatic coronary disease (myocardial infarction, percutaneous coronary intervention, coronary artery bypass graft surgery, or cardiac anginal chest pain in the past 6 months (180 days) prior to start of Screening) 20. History of acutely decompensated left heart failure or right heart failure within 90 days prior to Baseline, as per Investigator assessment 21. Significant (≥ 2+ \[or \> mild\] regurgitation) mitral regurgitation or aortic regurgitation valvular disease, or more than mild mitral stenosis or aortic stenosis valvular disease as seen on Screening ECHO 22. Started or stopped receiving any general supportive therapy for PH (e.g., oxygen, anticoagulants, digoxin) within 30 days prior to start of Screening 23. Use of supplemental oxygen \> 10 liters/minute or and SpO2 \< 90% while receiving typical oxygen supplementation, unless living at \> 1000 meters altitude above sea level in which SpO2 cannot be lower than 85% while receiving typical oxygen supplementation 24. Received intravenous (IV) inotropes (e.g., dobutamine, dopamine, norepinephrine, vasopressin) within 30 days prior to start of Screening 25. History of atrial septostomy within 180 days prior to start of Screening 26. History of portal hypertension or chronic liver disease, defined as mild to severe hepatic impairment (Child-Pugh Classes A to C) 27. Untreated, severe (defined as apnea hypoxia index of \> 30) obstructive sleep apnea 28. Active daily smoker of cannabis or tobacco 29. Current alcohol abuse or current illicit drug use 30. WHO Group 3 due to severe chronic obstructive pulmonary disease (COPD) or chronic pulmonary fibrosis and emphysema (CPFE) or PFT with FVC \< 50% or FEV1/FVC \< 65% or DLCO \< 25% (corrected for Hb g/dl) 31. Presence of lab abnormalities at Screening 32. History of greater than severe renal disease, including any episode of acute renal failure, with or without a prior history of renal disease in which acute dialysis (e.g., intermittent hemodialysis or continuous veno-venous hemofiltration) was required 33. Initiation of an exercise program for cardiopulmonary rehabilitation within 90 days prior to Baseline or planned initiation during the study (participants who are stable in the maintenance phase of a program and who will continue for the duration of the study are eligible) 34. Participants who plan to continue, or start during the study, medications which are sensitive cytochrome (CYP) 2D6 substrates with a narrow therapeutic index, such as nortriptyline, venlafaxine, and amitriptyline or CYP1A2 substrates with a narrow therapeutic index 35. History or presence of impaired cardiac function 36. Participants who plan to donate blood after signing consent for the study and for 28 days after their last dose of study drug Key Inclusion Criteria for Long-term Extension Period: 1. Participants must complete the main study period (defined as completion of assessments through the Week 24 visit) 2. Women of child-bearing potential (WOCBP) must have negative pregnancy test 3. All participants must comply with contraceptive guidance until 28 days after last dose of study drug for WOCBP and 90 days after the last dose of study drug for males Key Exclusion Criteria for Long-term Extension Period: 1. Participant withdrew from main study period due to an AE related to study drug 2. Female participant who is pregnant, breastfeeding, or intends to conceive during the long-term extension period 3. Males who do not agree to follow protocol contraception guidelines 4. Any condition that in the opinion of the investigator may pose a risk to the participant, interferes with the participant's participation or confounds assessments of the participant