If you want to import any external geometry files from other softwares so there are certain formats called neutral file formats, step IDs and para solid, these kind of formats. So these kinds of formats can be imported and can be exported to any software. So if we want to import that kind of stuff, go to File, you can see import external geometry files, so your piston that is STP format. Click ok. Once you have clicked, you can see the details of the body. And once you are done with that just generated you can see now right so This is how we can import external bodies into ANSYS design modeler.