Inclusion Criteria: Subject understands and has voluntarily signed and dated an informed consent form 1. Subject is male or female ≥ 40 years of age 2. Diagnosis of IPF is supported by HRCT and historical lung biopsy (surgical lung biopsy [SLB] or cryobiopsy) if available according to guidelines. 3. No features supporting an alternative diagnosis on transbronchial biopsy, bronchoalveolar lavage (BAL), or SLB, if performed. 4. Percent predicted forced vital capacity (% FVC) ≥ 45% and ≤ 95% at Screening 5. Percent predicted diffusion capacity of the lung for carbon monoxide (DLCO) ≥ 25% and ≤ 90% predicted at Screening. 6. Able to walk ≥ 150 meters during the 6-minute walk test (6MWT) at Screening 7. Females of childbearing potential (FCBP) must commit to true abstinence or agree to use two effective birth control methods. 8. Male subjects must practice true abstinence or use a barrier method of contraception. 9. Additional inclusion criteria apply. Progressive Pulmonary Fibrosis (PPF) Sub-Study: 1. Met all inclusion criteria described for IPF subjects other than Inclusion Criterion 5. 2. Features of diffuse fibrosing lung disease of > 10% on HRCT by central reading. 3. Investigator-documented ≥ 5% annualized relative decline in FVC in past 24 months from Screening Visit 1 Exclusion Criteria: The presence of any of the following will exclude a subject from enrollment: 1. Subject has any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from participating in the study. 2. Subject with a QTcF > 450 msec. 3. Evidence of clinically relevant airways obstruction at Screening. 4. Subjects using therapy targeted to treat IPF. 5. History of latent or active TB, unless there is medical record documentation of successful completion of a standard course of treatment 6. History of hepatitis B and/or hepatitis C, including those considered successfully treated/cured 7. Pregnancy or lactation. 8. Additional exclusion criteria apply.