3D FlipBook - Put behind paywall/categories issue

Hi, I’m trying to figure out how to get a pdf page behind a paywall. The issue I am having is, using the Paid Memberships Pro plugin, I need to be able to have the category from the post show up in my general categories section on Wordpress. I am pretty new to this stuff and was wondering if there is a way to link the 3D Flipbook categories with the WP categories or to just use the WP categories in a 3D Flipbook post. Or maybe if I could turn the book into a page so I could put it behind my membership plan? Is there any workaround I am missing?

I hope my question makes sense and I would really appreciate any help.