Okay, so i've just finished creating 4 technical manuals for a client, each of 80-140 pages, with diagrams, tables, formulae and walls of text. Its standard InDesign stuff, A4 layout, etc.

My client has come of out of the left field with a request for an 'interactive' version of the manuals for tablets (lets stick with iOS, for the moment).

Now I can do fancy pants interactive PDFs in my sleep but none of the cool stuff transfers when you view it in iOS. I found some workarounds to restore basic functionality but I think they want something a little...more....like zoomable pics, bookmarking links, etc

So, am I going to have to (somehow) write an app to get that done? I've done some googling and found a lot of book writing apps that seem to do what I want (but i've been burned before)...

Can anyone recommend a decent avenue of investigation that might do what i'm looking for? Turn content into something simple but heavily 'interactive'?