The best way to work with CDR graphics would be to of course use CorelDRAW, the very graphics suite that uses CDR format. But of course not every user has access to this somewhat expensive software, and have to rely on some 3rd party editing conversion tools.
Conversion to PostScript formats (.ps) is usually done for printing purposes. You can find 3rd party tools like UniConvertor or Inkscape that allows export to PostScript, but as always, using the original software is your best shot because of the compatibility.
Open CDR file Open PS fileA universal vector graphics translator
A vector graphics converter for various Linux distributions