I don't understand the existence of the Preview app on iPad. It's nearly exactly the same as what happens when you just open a PDF in Files. The benefit would have been if you could open files with Preview from 3rd party apps like Google Drive. While you can "export" a PDF to Preview from Google Drive, that creates a copy of the document, so now you have two versions of the same document, one stored in Google Drive, and the modified copy stored god knows where (either in a folder called On My iPad > Preview or in iCloud > Preview, but which one will it be? Both folders exist). Why can't we just open files, modify them, then save them back to where they were originally? Why the need to make copies of everything?
Also, open the Preview app, and you're greeted with this... weird abomination of an interface, with a random list of files at the bottom with no way to navigate "up one level". And if you press the "New document" button, a blank PNG gets created into the On my iPad > Preview folder. It doesn't even open or say anything, it just gets created. What the hell is this supposed to be?
Oh and Preview has no problem opening every single document in a brand new window, leaving you with countless versions of Preview open with random documents, that you now have to go find and close one by one. If you were on a Mac this would be fine, but with there being no desktop or window management, this becomes a ridiculous task.