Reply To: Where do I go from here? Epub? App?

I don’t have the answer that you need, but I do have to comments to make.

First, I’m not sure using multi-state objects is a good idea, due to support issues. You don’t know in what PDF reader your user will view the PDF, especially on mobile phones, and some PDF readers can strip out the all bells and whistles from the PDF rendering your ‘menu’ useless.

Secondly, I don’t think Adobe XD is a solution to this. As far as I know, XD is nothing more than an app wireframing tool.

It seems like what you need is a webpage optimized for mobile, or a mobile app (that might not get accepted in the Apple App Store because to the people at Apple this might not be considered an ‘app’).