I scrape popcorn ceilings and use a 4-inch utility knife or a drywall knife to chip away at the texture and create a smooth surface. I probably need to skim it with a thin layer of joint compound to smooth out imperfections, then I sand it smooth before repainting.
One more method is
Pre-taped Plastic Sheeting. Basically, one edge of the plastic sheeting already has tape attached. ...
This Backpack Style Sprayer is best to moisten the popcorn. Flexible Putty Knife to remove the popcorn.