rar is a type of compression of files. It is not an embroidery format. You need to unzip the rar and see what is inside of it. If you do not have a program to unzip the rar file, just google free rar unzipper. I use WINRAR, hope this helped.
You need to unzip the file first with an unzipping program like WinZip, ExtractNow. There are several programs. Once unzipped it should have your JEF file in the folder. If not, you can convert one to JEF.