Hello, suppose there's a vendor X who offers a plugin for 3ds max for non-commercial use. This plugin exports data to some file. This data is then loaded into our engine (probably converted to our own format first). Is this legal even if the engine is used for non-commercial purposes? Is the exported data/format copyrighted somehow?

If you're using the plugin as part of a commercial pipeline, you're essentially violating the TOCA. It's not about the file-format being protected, it's about using the plugin for a different purpose than it was designed.

Allan