By default, all software supports multiple file extensions. Google Reader supports at least 1 different file extensions. The basic files that Google Reader supports are .ATOM. However, not all of the extensions listed on the list are always used to save the effects of work in Google Reader. Very often, files with such extensions are used as source data files used by Google Reader.
Google Reader can be used to convert file formats between the file extensions listed below. You can open a file with one of the file extensions below via Google Reader and try to save it in another file format, also supported by Google Reader.