Users searching for obj to ai conversion are in most cases looking whether it is actually possible to import/use 3D models in Adobe Illustrator.
According to Internet sources, this is doable with proper plugin for Illustrator, for example with the free Cineware for Illustrator plugin. Once imported, you can work with the geometry of the model like usual. This topic is described extensively on Adobe Help pages, as well as in numerous guides and tutorials that can be found on the Internet. Many videos about Illustrator can be found on YouTube as well.
Updated: October 18, 2023