Yes, we have to replace the door frame when replacing the door.

There is no hard and fast rule, as each door frame is designed differently. However, in most cases it is advisable to replace the door frame when replacing the door. This is because the new door may be a different size or shape than the old one, which could cause the frame to warp or become misaligned.

It depends on the door frame and the door. In most cases, you don't have to replace the door frame when you replace the door, but it's always best to check with a professional to be sure.