The term you are looking for is 'Skimming'. A fine layer of plaster over the top of wallpaper covering the seams and cracks. Not a job for the inexperienced. Also you don't know what state the walls are in underneath the paper. You may do a rough skim and the weight of the plaster can peel it all off!
I have washable vinyl wall paper on my walls. The paper is in good condition but I would like to texture and paint the walls. Can I do this without taking the wall paper off?