qxf to qdf conversion is related to Quicken tax preparation software, considering both of these file types originate from it, albeit the first one is from Mac version and the other from the version for Windows.
It is quite possible that Quicken can export/convert data from the Mac version (.qxf) to files for Windows platform (.qdf) and this should be not a problem even in latest versions of Quicken. Further information about how to convert qxf to qdf can be found as Quicken website.