Apple’s Preview software does what 97% of their users need. It can open most PDFs, allow you to mark them up, and even fill some of them out. It is based upon the ISO 32000-2:2020 standard.
Unfortunately, Adobe keeps enhancing their own PDFs that don’t quite follow that standard. Most companies and software use Adobe’s APIs and software to create their PDF files. Something Apple doesn’t want to do.
I just use Preview and the built in OS stuff. I can generate PDFs, mock them up, convert them to JGPs when needed, etc. I don’t do a lot of stuff with them. If I need people to fill out forms and gather information, I use web based solutions like Google Forms, MailChimp, or SquareSpace Forms.
However, my big issue is iOS and iPadOS. The PDF is built into the OS itself. But, there’s no easy way to convert a PDF to JPG or straight obvious way to save a printout as a PDF. There are times I have to return to my Mac to handle PDF issues.
That’s where I really think Apple falls down: No Preview app for iOS or iPadOS.