Both RIFF and TIFF files are graphics images, albeit in completely different formats. RIFF format comes from Corel software, originally from a tool called Corel Painter, but now supported in apps from CorelDraw Graphics Suite. TIFF is a standard supported in pretty much every graphics editor.
This means that your best option how to convert riff to tiff is to use Corel software. Perhaps some 3rd party converters might support RIFF format as well, but overall the support for this graphics file type is very rare and if, it's usually labeled as RIF instead RIFF.
Updated: January 4, 2024