If it has never been painted, you can use a wide putty knife (wear a mask and safety glasses) and scrape off. If painted would be easier to go over it with 1/2" drywall and finish smooth. Need to find joist and screw into them.
I have heard it is not is matching difficult as it is a mess. I have popcorn ceilings and I keep procrastinating because of the mess that it will make.
It does make a mess AND I have found that around the areas where the sheetrock is joined, it is almost impossible to get that off. Mine had never been painted and I found it a chore that I wished I didn't start.
Very messy even when everything is covered in plastic. I used a spray bottle filled with warm water and 1/4 cup fabric softener, cheap stuff will work. Let water soften popcorn and scrape with wide putty knife. Lowe's or Home Depot carry a tool that holds a plastic bag to catch the popcorn while scrapping. I did not have problems w/sheetrock joints. Terrible chore but I was pleased with end results. Good Luck!
Impossible if it’s been painted a few times.