geo to obj conversion is certainly related to export of 3D models or graphics, but given the sheer number of different .geo files, it's hard to give a precise answer.
Some variants of VRML format use .geo extension, so this is certainly one possible venue for this conversion, but nowadays most users are looking for export of Houdini geometry files (geo) and that is actually topic of many tutorials and guides for Houdini, quiet often aimed at beginners. In this case geometry and particles can be exported to OBJ format.
Updated: October 13, 2023