Hello all...My friend have a problem to open a file in lower version of inventor.I send him some files, and He could't open them.I work in inventor 2010.How to save file in lower version.I know that this option have Auto Cad, but I could't find them in inventor.Thanks....

Unfortunately, this is not an option in Inventor (nor any other parametric 3D MCAD modeler). You have to use an generic data exchange format like STEP or SAT.