001 File Joiner & Splitter Pro allows you to easily join and split files of any size or kind. The files created have the extensions of .001,.002, etc. Have yup ever downloaded files with the .001 file format and wondered how to join them? All you have to do is double click the file with extension .001 and the rest of the file parts will be loaded into 001 File Joiner and Splitter Pro and will be joined together with a click of a mouse.