Update: I finally figured it out. This post helped: -discussions/pdf-downloaded-from-chrome-automatically-opening-.... Tl;dr: I had the new version of Acrobat disabled (purely because I hate it when software developers change the UI for no reason), and there's a bug in the old version that causes this. I enabled the new version and then disabled it again, and it isn't auto-opening pdfs anymore. I still don't have this checkbox in my settings, either in the new or old version of Acrobat, but at least I have a solution now.