OneNote on iPad

Hi everyone, I just bought the iPad Pro to use for school. I am used to using Microsoft OneNote o my MacBook and would like to start taking notes using it on my iPad to take handwritten notes with the Apple Pencil. However, I can not figure out for the life of me how to download PowerPoint slides from my school’s online drive (we use Moodle if you’ve heard of it) and then upload them to OneNote. I Googled the topic and it says there should be an option to download it like a PDF to iBooks, but that option does not seem to be showing up for me. Any help would be greatly appreciated. Thank you in advance!