The study is testing a drug called treprostinil, which people with progressive pulmonary fibrosis (PPF) will inhale to see if it helps them. Pulmonary fibrosis is a lung disease that causes scarring in the lungs. This study will last for 52 weeks, which is about one year. Participants will either receive the drug or a placebo, which is a substance with no active medication, and they will not know which one they are getting. They will start with a low dose and gradually increase as they can tolerate it. They will need to visit the clinic 6 times over the year. The study will check if the drug helps by measuring lung function, looking at overall survival, and checking how often the disease gets worse. Safety will also be watched closely by looking at side effects and other health checks. **Key Points:** - The study lasts for 52 weeks with 6 clinic visits. - Participants will inhale treprostinil or placebo 4 times daily. - Safety and lung function will be monitored throughout the study. It's important for potential participants to discuss with their doctors if they are interested and meet the study's criteria. Note: The decision to join should consider the time commitment and potential side effects.