As in ssid, use ePub if you need vector. If you need something that will be displayed the same under any conceivable circumstances, and still will be in many ye

As in ssid, use ePub if you need vector. If you need something that will be displayed the same under any conceivable circumstances, and still will be in many years, consider DJVU. I see DJVU mainly as a viable alternative for archiving, where people usually use PDF/A or TIFF (yes some still archive everything as TIFF).