Inclusion Criteria:

1. Subject voluntarily gave informed consent to participate in the study.
2. Males and females aged 18 years or older at the time of informed consent.

a. Females of reproductive potential were non-pregnant (as confirmed by a urine pregnancy test at screening) and non-lactating, and: i. Abstained from intercourse (when in line with their preferred and usual lifestyle), or ii. Used 2 medically acceptable, highly effective forms of contraception for the duration of study, and at least 30 days after discontinuing study drug.

b. Males with a partner of childbearing potential used condoms for the duration of treatment and for at least 48 hours after discontinuing study drug.
3. The subject had a confirmed diagnosis of WHO Group 3 PH based on computed tomography (CT) imaging which was performed within 6 months prior to randomization and demonstrated evidence of diffuse parenchymal lung disease. Subjects had any form of ILD or CPFE.
4. Subjects were required to have a right heart catheterization (RHC) within 1 year prior to randomization with the following documented parameters:

1. Pulmonary vascular resistance (PVR) \>3 Wood Units (WU) and
2. A pulmonary capillary wedge pressure (PCWP) of \<15 mmHg and
3. A mean pulmonary arterial pressure (mPAP) of \>25 mmHg
5. Baseline 6MWD ≥100 m.
6. Subjects on a chronic medication for underlying lung disease (ie, pirfenidone, nintedanib, etc) were on a stable and optimized dose for ≥30 days prior to randomization.
7. In the opinion of the Investigator, the subject was able to communicate effectively with study personnel, and was considered reliable, willing and likely to be cooperative with protocol requirements, including attending all study visits.
8. Subjects with connective tissue disease (CTD) had a Baseline forced vital capacity (FVC) of \<70%.

Exclusion criteria:

1. The subject had a diagnosis of PAH or PH for reasons other than WHO Group 3 PH ILD as outlined in Inclusion Criterion 3.
2. The subject showed intolerance or significant lack of efficacy to a prostacyclin or prostacyclin analogue that resulted in discontinuation or inability to effectively titrate that therapy.
3. The subject received any PAH-approved therapy including: prostacyclin therapy (ie, epoprostenol, treprostinil, iloprost, or beraprost; except for acute vasoreactivity testing), prostacyclin (IP) receptor agonist (selexipag), endothelin receptor antagonist (ERA), phosphodiesterase type 5 inhibitor (PDE5-I), or soluble guanylate cyclase (sGC) stimulator within 60 days of randomization.
4. The subject had evidence of clinically significant left-sided heart disease as defined by:

1. PCWP \>15 mmHg
2. Left ventricular ejection fraction \<40%. Note: Subjects with abnormal left ventricular function attributable entirely to impaired left ventricular filling due to the effects of right ventricular overload (ie, right ventricular hypertrophy and/or dilatation) were not excluded.
5. The subject was receiving \>10 L/min of oxygen supplementation by any mode of delivery at rest at Baseline.
6. Current use of any inhaled tobacco/marijuana products or significant history of drug abuse at the time of informed consent.
7. Exacerbation of underlying lung disease or active pulmonary or upper respiratory infection within 30 days of randomization.
8. Initiation of pulmonary rehabilitation within 12 weeks prior to randomization.
9. In the opinion of the Investigator, the subject had any condition that would interfere with the interpretation of study assessments or has any disease or condition (ie, peripheral vascular disease, musculoskeletal disorder, morbid obesity) that would likely be the primary limit to ambulation (as opposed to PH).
10. Use of any investigational drug/device, or participation in any investigational study with therapeutic intent within 30 days prior to randomization.
11. Severe concomitant illness limiting life expectancy (\<6 months).
12. Acute pulmonary embolism within 90 days of randomization.