PDFs exist to emulate paper (a need which won't totally go away), but maybe it would be nice if the format and authoring tools supported a sort of alternate ren

PDFs exist to emulate paper (a need which won't totally go away), but maybe it would be nice if the format and authoring tools supported a sort of alternate rendering mode that is online-friendly. So for example, a word processor may be set to produce two-column text, and for paper that makes sense ergonomically. But it is horrible in combination with scrollbars. The same goes for margins at the top and bottom of pages. A typical word processor allows you to easily switch text to one-column mode or adjust the page margins, so with just a few changes it could render your document in a more online-friendly way. So when you save as PDF, it would be neat if it could include both renderings into the same document. In this hypothetical world, the PDF viewer would then decide whether to render it in faithful-to-paper mode or in online-friendly mode.