I agree with the comments pointing out that PDF was not primarily intended for screen usage. However, it’s quite a good format for typeset text. What if the pro

I agree with the comments pointing out that PDF was not primarily intended for screen usage. However, it’s quite a good format for typeset text. What if the problem is not really with the format itself, but the way it us used? What if the PDF file was customized to the specific device they will be opened on? It would probably not be impossible to take EPUB source and then convert to PDF via (La)TeX, with good typograhic settings for the specific device. For my laptop screen the page would be around 28 centimers wide, perhaps set in three or four columns. For my smartphone, one column is enough. With this setup one would not have to scroll up and down while reading the columns, which is the case now when reading e.g. scientific papers. And because of the great quality of the TeX engine it might be easier to achieve a good layout than hacking around with HTML/CSS/Javascript.