missing object lines converting from inventor drawing to autocad dxf file

hello - i was required to convert an inventor drawing to autocad dxf file by a customer - when the inventor drawing was saved as a dxf then the dxf was opened all the text, dimensions and object lines were there - if the inventor drawing was saved to and autocad file then made a dxf only the object lines were missing- all layers, viewports and everything else was turned on - when switching from paper space to model, model space was empty - the customer was able to read the dxf fortunately but for future use how can i prevent this - any help or info would be greatly appreciated - thank you