In Windows 7 and above, files within folders appear with a name beneath the icon, but without the file extensions. While the icon will show the user what file extension each document has, some users prefer to have the file extension visible on every file. This is ideal for people who have folders full of files that have the same icons as a result of being opened in the same applications, but which have different extensions.
Read More at:https://appuals.com/how-to-display-file-extensions-in-folders-in-windows-7-above/