This article explains all the different file formats that use the KEY file extension. It also explains how to open and convert them, if possible.
Using a key file for encryption
A file with the .KEY extension can be either a plain text or an encoded generic license key file used to register a software program. Different applications use different KEY files to register their respective software and prove that the user is the legal purchaser.
A similar file format uses the KEY file extension as a way to store general registration information. It is likely created by the program when a product key is used, and can potentially be transferred to other computers, should the user need to reinstall the software elsewhere.
Another type of KEY file is a Keynote Presentation file, which is created by the Apple Keynote software. This is a type of presentation that may contain slides with images, shapes, tables, text, notes, media files, XML-related data, etc. When stored in iCloud, ".KEY-TEF" is used instead.
