Assuming Microsoft Widows here, there are two ways to hide file extensions.
1. In the Windows Explorer Folder Options find the “Hide extensions for known file types” and un-check it.
2. In the registry, within HKCR a key can be set that will always hide the extension of a file type. In this key a value can be set to hide the file extension called “NeverShowExt” for the file type.
So, if someone wants to always hide a file extension they can create a file type entry in HKCR and set the “NeverShowExt” value to hide it. You can remove the “NeverShowExt” value to have the extension seen.