Implement an option via settings to choose between vertical (up/down) or horizontal(left/right) page scroll.
Do you mean on iPad or iPhone? Both?
Do you think in this case the page should be not taller than the screen height?
This is only important for me for the iPad. I'm not sure I understand your question about screen height. Preferably I would be able to horizontally scroll to the next page and retain the same level of zoom that I was using on the previous page. Also, it would be helpful if the next page were automatically at the same level of right/left pan as the previous page, and panned vertically to the top. This way I can retain my level of zoom and go automatically from the bottom of the previous page to the top of the next page.
It might be helpful to look at the app PDF Expert, which implements this behavior quite well. But even without the zoom and pan considerations, simply having horizontal scroll would be great. Thanks!