find compatible apps for an older ipad

i'm still using an older ipad, version 5.1.1 & model mb292ll.

i'm having a tough time tracking down a free pdf viewer that both allows me to write onto the pdf file and is also compatible with my tablet.

"app store" lets me filter the searches by release date but not organized ascending/descending, so it takes a while to just scroll toward the end. once I get to an app that might work, i check it out, but hitting the "back" button takes me back to the beginning of the search results, so it's a pretty time-intensive process.

short of spending a ton of time doing that, are there any options for finding that type of app? is there any way i can download a compatible app and load it onto my ipad through my computer? i'm imagining something like oldversion.com for apps, but i have no idea if that exists.

my computer is a pc, if that makes a difference.

also, any app suggestions would be appreciated, but i don't mind doing the legwork there.

thanks