A bit of warm water and a scraper. You'll want to get the old pad good and wet, and then scrape if off the floor. Obviously, this can be a tricky deal on a wood floor, as too much water and a wood floor do not mix AT ALL. You don't want to ruin the very thing you're trying to salvage.
I actually found that, although it's messier, it was safer for me to use a power sander WHILE WEARING a respirator. Do not breath that nasty stuff... all kinds of bacteria.