The installer tapes the carpet together with a hot iron made for that purpose. It's like a hot glue gun. Sometimes they will also sew it but probably not at a door.

So use a sharp utility knife, find the seam and cut the tape under the carpet. This will be easy if you've already pulled the carpet up.

Take the carpet outside and lay it on a patio or driveway. It will dry pretty quick in the hot weather. You could also cut out the wet pad and dry that but it will take longer so if you don't want to fool with it, replace it. The pad may be glued or stapled down so it will tear it up to remove it anyway.

You can rent a carpet iron and retape the seam when you put it back in. Also a knee kicker if you need to re-stretch the carpet. If it's just a room, you can probably hand stretch it good enough and not have to trim it, just put it back.

Look up some videos online, probably show how to do it all.