obj to x3d conversion is typically searched by users that are exploring options how to either convert 3D objects (.obj) directly to X3D models, or to which software import .obj files so they can be exported as .x3d files.
Blender is most likely your best choice. You can download it for free, it should support both of these file types and last but not least, you can find many guides and tutorials for it on the Internet. This can be useful if you struggle with the export somehow or face another issue.
Updated: September 14, 2023