LF files contain license information created by SoftwareKey System. This XML-formatted text registers software applications. The LF file extension indicates which app can open the file. Different programs may use LF files for different data types. Unless developing software, you likely should not open or edit LF files. To open an LF file, an appropriate program that supports the format must be installed. We provide a list of programs supporting LF files. Download and install any of these programs. Then LF files should open automatically with the installed application. The Windows message “How do you want to open this file?” or “Windows cannot open this file” appears when lacking proper software. Right-click or long-press the file to choose a program if this happens. In Linux, LF file manager provides a minimalist console interface to view directory hierarchy in terminal. Use “Online LF Text Viewer” to analyze contents of an LF file. Be cautious when opening LF files from unknown sources, including potential malware.