By default windows does not display file extensions for known file types. It is often useful to see extensions especially with regard to MS office’s file extension incompatibility.
If your files do not have extensions such as in the above picture, do the following:
1. Press Alt, this will show the menus.
2. Click on the tools menu and choose Folder options.
3. Click on the View tab (second tab).
4. Un-tick “Hide extensions for known file types”.
5. Click OK and OK to return to the folder.
Files will now have their extensions displayed.