The best way to work with CDR graphics is to use the default software for this format - CorelDRAW graphics suite. However, not all users have access to this somewhat expensive software, and have to rely on some 3rd party editing conversion tools.
DXF is a vector based format mainly used for CAD drawings. Some shapes saved in CDR format can be exported and saved to this generic format, which is what cdr to dxf conversion represents - export of vector graphics from .cdr files to DXF format.