Study LTI-401 is an open-label, multicenter study which will evaluate the safety and tolerability of LIQ861, the study drug, in subjects who have World Health Organization (WHO) Group 1 & 3 Pulmonary Hypertension. The purpose of this research study is to evaluate the long-term safety and tolerability of LIQ861 in patients with WHO Group 3 Pulmonary Hypertension associated with interstitial lung disease (PH-ILD). The investigational form of Treprostinil in this study is called LIQ861, it is delivered to your lungs using a hand-held device called a dry powder inhaler (DPI). Dose levels may be adjusted by the Study Doctor between 26.5 micrograms to 318 micrograms based on your PH-ILD symptoms. The study will include approximately 60 subjects and participation will last 52 weeks.