This study is about testing **inhaled treprostinil**, a medication, for people with **progressive pulmonary fibrosis (PPF)**, a lung disease where lungs become scarred. The study will last for 52 weeks (1 year).

Participants will receive either the medication or a fake treatment called a **placebo**. The study is **double-blind**, meaning neither the participants nor the researchers know who gets the real medication. They'll start with 3 breaths of the treatment 4 times a day and increase to 12 breaths as they can handle it.

Participants need to visit the clinic 6 times over the year to check how they're doing and ensure safety, looking at lung function and side effects. After the study, they might join an **open-label extension (OLE)**, where everyone gets the real medication.

• Duration: 1 year with 6 clinic visits.
• Treatment: Inhaled treprostinil or placebo, 4 times daily.
• Eligibility: Adults with PPF, not pregnant, and willing to use contraception if needed.