Inclusion Criteria: 

• Female subjects must be surgically sterile, postmenopausal (minimum 1 year without menses), or agree to use 1 or more forms of highly effective contraception from the time of signing of the informed consent form (ICF) until 3 months after the last injection of study medication. Male subjects must also agree to use 1 or more forms of highly effective contraception for either themselves or their partners from signing of ICF until 4 months after last injection of study medication.
• IPF diagnosed based on modified ATS/ERS/JRS/ALAT IPF guideline for diagnosis and management, within 3 years of Screening. 
• Combination of high-resolution computed tomography (HRCT) pattern and, if one has been obtained, surgical lung biopsy pattern, consistent with diagnosis of IPF.
• Carbon monoxide diffusion capacity (DLco) (corrected for hemoglobin): 30% to 79% predicted of normal at Screening, with no clinically significant deterioration between the Screening Visit and randomization, as determined by the Investigator. 
• Forced (expiratory) vital capacity (FVC) ≥50% predicted of normal at Screening, with no clinically significant deterioration between the Screening Visit and randomization, as determined by the Investigator.
• If a subject is taking nintedanib or pirfenidone, they must be on a stable dose for at least 8 weeks prior to randomization.

Exclusion Criteria:

• Unable to perform pulmonary functional tests (PFTs) or undergo HRCT procedure. 
• Peripheral capillary oxygen saturation (SpO2) <90% at rest (if on oxygen supplementation, must be ≤2 L/min at rest). 
• Airway obstruction (i.e., prebronchodilator FEV1/FVC <0.7) or evidence of a bronchodilator response as defined by an absolute increase of ≥12% and an increase of ≥200 milliliters (mL) in FEV1 or FVC, or both, after bronchodilator use, compared with the values before bronchodilator use at Screening. 
• End-stage fibrotic disease likely requiring organ transplantation within 12 months, or if the subject has initiated active evaluation for organ transplantation. 
• The extent of emphysema in the lungs exceeds fibrosis, based on central review of HRCT scans. 
• Body weight <60 kg at Screening. 
• History of or ongoing malignant disease, including solid tumors and hematologic malignancies, with the exception of basal cell carcinomas, squamous cell carcinomas, and carcinoma in situ of the cervix that have been completely excised and considered cured >2 years prior to Screening.
• Significant cardiac disease (e.g., New York Heart Association Class 3 or 4; myocardial infarction within the past 6 months; unstable angina; coronary angioplasty or coronary artery bypass graft within the past 6 months; uncontrolled atrial or ventricular cardiac arrhythmias; or pulmonary hypertension requiring pharmacologic treatment). 
• Clinical diagnosis of any connective tissue disease (including but not limited to scleroderma, polymyositis/dermatomyositis, systemic lupus erythematosus, and rheumatoid arthritis) or a diagnosis of interstitial pneumonia with autoimmune features as determined by the Investigator. 
• Other disease that may interfere with testing procedures or, in the judgment of the Investigator, may interfere with study participation or may put the patient at risk when participating in this study. 
• Other unspecified reasons that, in the opinion of the Investigator or Biogen, make the subject unsuitable for enrollment.
  • NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.