Besides images, I think we handle and use PDF files the most. PDF (Portable Document Format) is ubiquitous, everyone uses PDF’s at least some of the time. The macOS has had the builtin Preview App for handling PDF’s for a long time. The earlier versions of Preview were pretty weak as far as capabilities go, but no more. This excellent video shows how to use several sophisticated features of the Preview App. I will bet you did not know it would do some of these things. Yes, you can get third party Apps for handling PDF files, but maybe you do not need to do so.