If you make your PDFs in A5, you can print two of them on an A4 paper and read the paper in landscape orientation. For the same reasons the size fits well for d

If you make your PDFs in A5, you can print two of them on an A4 paper and read the paper in landscape orientation. For the same reasons the size fits well for displaying on a computer screen and on a tablet/e-reader. It's still a bit too big to squeeze down to a cell phone, but at least better than A4/Letter size. As for responsive HTML, it's the responsibility of the designer to make it work if he/she is worth their salt. Like you say, HTML without CSS is already responsive. If businesses understood that there are a big segment of customers who will always use their computer and never their phone when it's time to make a purchase, perhaps they'd be better at it.