Showing file extensions in Windows makes the real file type visible, which reduces the chance of opening a disguised executable and helps spot misleading double extensions. Keeping extensions visible also makes renaming, searching, and troubleshooting more predictable by showing complete filenames.
File extensions are the suffix after the final dot in a filename, such as .txt, .jpg, or .exe, and they influence default app associations. File Explorer can hide extensions for known file types, but that only changes what is displayed in the file list, not the underlying file.
The option is saved per user and applies across folders opened in File Explorer. Changing an extension does not convert a file’s contents and can break app associations, so keep extensions visible and rename carefully when needed.
On Windows 10, open the View tab and enable File name extensions.
Double extensions like invoice.pdf.exe become obvious when extensions are shown.