The purpose of this study is to evaluate the potential usefulness of pamrevlumab in IPF, compared to placebo (a substance that looks like the investigational drug, but has no active agent). The total duration of your involvement on the study will be approximately 60 weeks. If you meet the entry criteria (requirements) and decide to participate in this study, you will be randomly assigned to 1 of 2 treatment groups: Arm A: Pamrevlumab or Arm B: Placebo. The study includes clinical visits. Approximately 565 subjects will participate in this study at approximately 200 research sites globally.