A wireless data processing device 2 stores partially completed versions of a file needed to replace a current version of a file used by that target device 2. When a device storing a more up-to-date version of the file than the current complete version stored by the target device 2 moves into range, downloading of that new version either completely, or resuming from a previously reached point, is initiated. When the in-range device has more than one version of the file that could be downloaded, the version selected for initial download may be the one which will take least time to complete.