Was the padding actually glued to the floor or it's just become stuck in places because of time and pressure of furniture and people walking on the floor? I ask because when I've removed carpet in my house, the padding has needed scraping in places, but it wasn't that bad. A wide putty knife worked well. If it really was glued, I think you'll still have to scrape off as much as possible and then use an adhesive solvent to get the rest of it cleaned off. Stinky chemical stuff, but it'll work.