Convert CATDRAWING to CATPART

CATDRAWING and CATPART formats originate from CATIA software from Dassault Systemes, which means this software is your best choice for handling these files. Alas, it doesn't look like these two formats can be converted between each other, because they serve different purpose and contain different CAD data, but perhaps some kind of export is doable.

Simply put, it is impossible to convert CATDRAWING to CATPART directly.
Thus, there is no so-called catdrawing to catpart converter or a free online .catdrawing to .catpart converter to be found.