OFF is older, yet in some software still used 3D object polygon based format and supported in some 3D modeling tools, viewers or converters. As such it should be possible to convert OFF format to the STL 3D printing format (stereolithography), with several dedicated 3D modeling converters like IVcon or meshconv.
Open OFF file Open STL fileA Mac version of the popular 3D visualisation software
A converter for 3D formats
A command line converter for 3D format
A 3D mesh converter
A free online 3D model conversion service