I have spent a lot of time trying to integrate PDFs into my website. There are hundreds of PDF forms that I need to be able to display to visitors in various dynamic ways, and the functionality just isn’t there. PDFs are as ubiquitous as PNGs and JPGs, so lets give them the love and attention they deserve.
They should be able to live in the Media Library. They are media. No one wants to create CPTs and custom fields for PDFs.
They should get a nice, high quality thumbnail / feature image that can be displayed in query loops.
Okay. Literally that should be it. Like PDFs should just be like image assets except that their image is just the thumbnail of their first page and clicking on 'em will take you to the full PDF. Throw in a convenient Download option if you want to be overachievers, but really just basic PDF functionality would make my day.