Can You Paint Over Wallpaper Sizing. Generally it is not considered as a good idea to prime over wallpaper sizing. Yes with some exceptions and considerations you can paint over wallpaper.
Check out this guide to painting over wallpaper glue. Wallpaper doesnt stick to your wall it sticks to the paint on your wall. This is done either using brushing on size or a dilute mix of wallpaper paste - most packets will give the details of mixing for sizing.
Of course the first few steps up until sizing can be followed like the painting blog.
If your wallpaper is in good condition without peeling areas and holes try painting over it instead of replacing it for a fresh new look. Latex paint is often porous allowing the wall to breathe. Heres how its done. Something thats worked really well for me in dealing with the nightmarish residual wallpaper glue and peeling drywall is this.