[Dylrob]

May third party apps let you transfer files into them from your iCloud Drive, which can be accessed on the PC via any web browser. (Hell, you can play files directly from iCloud Drive, the only problem being that it won’t save your progress)

Goodreader is a really powerful app with multiple input/output methods built-in. I’ve been using this to get aroun the limitations in iOS since long before iCloud Drive was even a thing. (Despite the name, it handles video and audio as well, the latter of which can be easily organized into tracks just by placing them in the same folder)