The filename extension does not appear on all files, Windows XP hides the extension for known file types.
In order to go through the laborious procedure of always having to open the properties, the folder option can be opened in the Extras menu and switched to the View tab. There, the Hide Extension option can be deactivated for known file types. After clicking on Run, all extensions are displayed.
With the key combination “Alt” and simultaneous double click on file, the properties also open.