JPEG2000 (.jpf) has been once the supposed successor of the common JPEG format (.jpg, .jpeg), but it didn't gain popular support, certainly not as a common standard. Yet some graphics editor support it and allow users to re-save or convert these graphics files to other formats, including original JPEG. Such jpg to jpef conversion will however remove the unique properties of JPEG2000 and make normal image.
Open JPF file Open JPEG file