I really appreciate the feedback so far. Slowly but surely I'm getting a sense for what I'm up against and how I might want to proceed.
I had a fairly long talk with one of the two main people who is putting the website together. His take is that PDFs are fine for people to download from the website, so he doesn't think it would be worth all the extra labor to try to convert what I have to an e-book format. He said that as far as the president of the group's concern that PDFs are unappealing and awkward to read compared to an e-book, that's likely because he's downloading them to his tablet as a PDF whereas if he pushed a different button the same file on the same tablet could be read more like an e-book.
He did say that moving forward if we want to do future content as an e-book that we would need to take that into account from the start, and so my approach would be very different from what it was this time when I was basically creating a print booklet. He says it's much easier to create an e-book from the beginning than to go back after the fact and convert something else to an e-book, which makes sense.
The president may or may not go along with his suggestion that we leave this one as a PDF, so right now I don't know if I'll need to try to convert what I have to an e-book file type. If it turns out I do, I think the responses in this thread will get me going in the right direction. Not that I currently know how to do all the steps that have been suggested, but at least I have the general approach now, and I can try to teach myself each step, in part by searching this site. Or maybe I'm being too optimistic that I'll be able to do that, but we'll see.