Windows: File Extensions

A "file extension" is an identifier, beginning with a period, specified as a suffix to the name of a computer file. For example:

    .txt
    .pbn
    .js

The file extension specifies the "type" of the file, which is used to determine the icon shown for the file, the program that is used (by default) to open the file, and so on.

Unhiding

By default, most file extensions are hidden. To show them, you must use the "Folder Options" panel. In Windows 11, use File Explorer, click "..." to see the menu, and then click "Options". In Windows 10, use the File Explorer "File→Options" menu command. In Windows 7, use the Windows Explorer "Organize→Folder and search options" menu command. There are also several other ways to access this panel, such as using the Windows Start menu (or the taskbar) to search for "folder options".

In Windows 10 and 11, this same panel is also known as "File Explorer Options".

In this panel, select the "View" tab:

Folder Options panel

Find and un-check the "Hide extensions for known file types" option (second from the bottom in the screenshot above). Then click "OK".

Changing

To change a file's extension, just perform a "rename". To do this, in File Explorer, click on the file name (not its icon). An edit box will open for the filename:

File Rename edit box

(Notice that in the edit box, the name part is selected and the extension part is not, just the opposite of what you want. Oh well.)

Use the mouse and keyboard as you would in any edit box to select and change the extension part, and then press the Enter key.

You will receive a warning message: "If you change a file name extension, the file might become unusable. Are you sure you want to change it?". Answer "Yes".