eps to pat conversion is most likely used for either recovery of Corel vector graphics from previously export EPS files (Encapsulated PostScript). Or perhaps even direct conversion of EPS content to CorelDRAW vector pattern format (.pat).
In either of these cases, you will need CorelDRAW, because it is the only software that can be used to create this type of .pat files.
Of course numerous different formats use .pat extension, so it might be very well possible that other similar conversions exist as well.