While most commercial painters would not recommend painting over the old wallpaper in your office building, there is nothing that says you could not do it. Most old wallpaper, however, tends to have a sort of slick surface, and it can start to shrivel under the wetness of the paint. Ergo, you should know before you attempt to tackle this job on your own that there are steps to painting over old office wallpaper.
Getting That Wallpapered Office Space Ready
If at all possible, remove the furniture prior to completing all of the following steps. Movable cabinets and shelving should be taken down and temporarily relocated. All of the old wallpaper should be exposed before you start so that you can see exactly what you need to do and how to get into tough-to-reach areas.
Use painter's tape to tape off edges of cabinets, door frames, and even baseboards, if you do not intend to remove the baseboards. Cover the floor with a clear tarp to protect it from paint, plaster, and spackling. Now you are ready for the real work.
Rough up the Wallpaper
Roughing up the wallpaper with a sander creates holes in the paper. These are the areas where the wallpaper was already weak and crumbling, and you just could not see it. By creating a rough surface on the wallpaper to start, your next step, plastering, will stick better.
Spray-on Plaster and Spackling
As far as the plaster process is concerned, you do not want a thick, heavy plaster. It will not adhere well to the roughened wallpaper. Eventually, such a mistake would be costly as you watch thick chunks of plaster backed with bits of wallpaper fall from the walls. Instead, use a spray-on plaster/spackling mix. The spackling paste in the spray causes the plaster to adhere better to the wallpaper, while still providing you with the necessary plaster covering you need prior to painting.
Finally, after the spray-on plaster and spackling have sufficiently dried (this may take a few days to a week), you are ready to paint the office walls. An even and steady paint sprayer tool is highly recommended for a beginner as the paint will be spread evenly across the walls and ceiling (if applicable; some people do not paint the ceiling). The detailing in this job requires an edger, small brush, and/or small detail roller to get paint up close to door frames and cabinetry, if there is cabinetry built into your office building's rooms.
Contact a commercial painter for more help.