hsf to png conversion is typically used for the purpose of exporting textures out of HOOPS 3D graphics files, or making a picture previews of the visualized models.
HSF format has been introduced in 90s and is not that common nowadays for modern content, which means the real issue with be with to find a tool that still supports this format. Many modern software (including CATIA or SolidWorks) require plugin to support HSF format.