By default, File Explorer in Windows 10 does not show the file extension for most file types. You can enable file extensions for files in File Explorer options. To quickly toggle hiding or showing file extensions, you can add a special context menu entry.
Tag: Windows 10 Show File Extensions
How to Show or Hide File Extensions in Windows 10
By default, File Explorer in Windows 10 does not show the file extension for most file types. This is a security risk as anyone could send you a malicious file named "Runme.txt.exe" but Windows will hide the .exe portion, so an inexperienced user can inadvertently open the file thinking that it is a text file and malware will infect his or her PC.
