I have two similar requests:

I am a private tutor so I usually have a couple of standard documents open on my iPad all the time (e.g. PDF of the periodic table). When I close the app (not minimise) or when I press the x button by mistake, I need to re locate it in my folders. I know I can 'favourite' it but it would be so much easier if there is an option to pin it (sort of like in Safari/other web browsers where you can pin open windows). That way it will always open when I open the app, and I can't accidentally close it.

The second is similar. I often keep documents open for a while (i.e. more than a week). I have multiple students in a night so I often open about 30 different documents. When I accidentally close a document I often don't know which one it was until I have to go find it again. The feature of 'recently opened documents' doesn't work because it isn't a recently opened document - I opened it over a week ago and opened many more after. If there is a way to undo the closed tab when it is accidentally shut that would be so helpful thank you!