DWF AutoSave saves the copy of the  Autodesk® Inventor®  drawing automatically to DWF(x) during save command. The file is saved in the same folder as the original drawing with the same file name. 

See detailed information here, www.codesystems.fi/products/?product=cSysDwfAutoSave

Note! DWF AutoSave works only when drawing is saved after modification. So it does not make a DWF(x) if drawing has not changed.