Evaluate the Safety and Efficacy of FG-3019 (Pamrevlumab) in Participants With Idiopathic Pulmonary Fibrosis (IPF)

Inclusion Criteria: 1. Age 40 to 80 years, inclusive. 2. Diagnosis of IPF as defined by current international guidelines. Each participant must have 1 of the following: (1) Usual Interstitial Pneumonia (UIP) Pattern on an available high-resolution computed tomography (HRCT) scan; or (2) Possible UIP Pattern on an available HRCT scan and surgical lung biopsy within 4 years of Screening showing UIP Pattern. 3. History of IPF of ≤5 years duration with onset defined as the date of the first diagnosis of IPF by HRCT or surgical lung biopsy. 4. Interstitial pulmonary fibrosis defined by HRCT scan at Screening, with evidence of ≥10% to \<50% parenchymal fibrosis (reticulation) and \<25% honeycombing, within the whole lung, as determined by the HRCT central reader. 5. FVC percent of predicted value ≥55% at Screening. 6. Female participants of childbearing potential (including those \<1 year postmenopausal) must be willing to use a medically acceptable method of contraception, for example, an oral contraceptive, depot progesterone, or intrauterine device. Male participants with female partners of childbearing potential who are not using birth control as described above must use a barrier method of contraception (for example, condom) if not surgically sterile (for example, vasectomy). 7. For sub-study only: Receiving treatment for IPF with a stable dose of pirfenidone or with a stable dose of nintedanib for at least 3 months before Screening initiation and willing to continue treatment with pirfenidone or with nintedanib according to the corresponding approved label and the prescribing physician, including all listed safety requirements (for example, liver function tests, avoidance of sunlight and sunlamp exposure and wearing of sunscreen and protective clothing daily for pirfenidone, and smoking cessation). Exclusion Criteria: 1. Women who are pregnant or nursing. 2. Infiltrative lung disease other than IPF, including any of the other types of idiopathic interstitial pneumonias (Travis, 2013); lung diseases related to exposure to fibrogenic agents or other environmental toxins or drugs; other types of occupational lung diseases; granulomatous lung diseases; pulmonary vascular diseases; systemic diseases, including vasculitis and connective tissue diseases. 3. HRCT scan findings at Screening are inconsistent with UIP Pattern, as determined by the HRCT central reader. 4. Pathology diagnosis on surgical lung biopsy is anything other than UIP Pattern, as determined by the local pathologist. 5. The Investigator judges that there has been sustained improvement in the severity of IPF during the 12 months prior to Screening, based on changes in FVC, diffusing capacity of the lung for carbon monoxide (DLCO), and/or HRCT scans of the chest. 6. Clinically important abnormal laboratory tests. 7. Upper or lower respiratory tract infection of any type within 4 weeks of the first Screening visit. 8. Acute exacerbation of IPF within 3 months of the first Screening visit. 9. Use of medications to treat IPF within 5 half-lives of Day 1 dosing. If monoclonal antibodies were used, the last dose of the antibody must be at least 4 weeks before Day 1 dosing. This applies to participants enrolled in Main Study only. 10. Use of any investigational drugs, including any investigational drugs for IPF, within 4 weeks prior to Day 1 dosing. 11. History of cancer diagnosis of any type in the 3 years preceding Screening, excluding non-melanomatous skin cancer, localized bladder cancer, or in situ cancers. 12. Diffusing capacity (DLCO) less than 30% of predicted value. 13. History of allergic or anaphylactic reaction to human, humanized, chimeric, or murine monoclonal antibodies. 14. Previous treatment with FG-3019. 15. Body weight greater than 130 kilograms.