The easiest way how to achieve riff to cdr conversion is to import your .riff files to CorelDraw and save these in the default CDR format. Considering both formats are from Corel, this might actually be one of the very few options how to convert riff to cdr. To make things a bit worse, there are several variants of RIFF format and not every type might be supported.
Updated: September 5, 2023