Think about it: You can't get files on your device in a useable format anymore. This means piracy becomes exponentially harder to consume (i.e. you can't use your iPad [easily] as a reader for your pirated ebooks). Quite honestly, that's a stroke of genius and likely a secondary motivation for this workflow.
I do this all the time. For me, it's convenient to use Dropbox as the intermediary, but there's plenty of other ways too.
Whether pdf or epub, and whichever device or type of device you use to add the file, once you do it will automatically be stored in your icloud and synced across devices. Same as any purchase.
I can later open up the iOS file manager and find the mp3 for my new favourite song in my music player's folder, click Share and send the file to my friend on Telegram or whatever.
iPhones are pretty reasonable piracy tools now.