We have a curved opening between the entrance and bedroom/study. Since we would like to use this room as a bedroom and the opening is in the main entryway, does anyone have suggestions for closing this opening? It is large and curved, finished drywall with paint.
I'm presuming by curved opening, you are referring to the top of the doorway where the header would be.
To install a door, you'll have to get a rough opening, and while doing so, it will probably be easiest to square off the top of the opening. You'll lose the style of the opening, but the easiest solution is frequently the cheapest, too.
For enough money, you could also get a custom door made. However, depending on the height, you could also install a thin header across the top of the door frame and close off the opening over the door with glass, curtains, etc.
And one final idea is that you could extend the doorway into the room, framing out a new wall a foot or so inside the opening for the doors. The arched opening would remain with the door(s) set inside. If this creates a nook on one or both sides of the door, you can create some built in shelves. I'd only do this if your home has a formal look and this is the master bedroom.