prt to cgr conversion is almost certainly related to export of 3D CAD part files (often saved as .prt) to CATIA format (.cgr), or import of .prt files to CATIA.
It's not easy to give specific answer for this, considering the large number of different CAD part format formats use prt extension, but the most common ones are probably supported in CATIA.
You can always take advantage of some of the dedicated 3D model converters though.
Updated: September 27, 2023