What is an EXTR file? An EXTR file is an encrypted folder used by COW, which is an operating system for select mobile devices based on Linux that was discontinued before being released to the public. It contains a program and a Main.py script that stores instructions for where the COW system installer should install the program. EXTR files are downloaded to a mobile device from the COW App Store and then decrypted and opened automatically by the COW system when installing the downloaded program.

More Information Since the COW operating system is no longer developed, you will not encounter COW App Extractor EXTR files. If you do come across a file with the .extr file extension, it is saved in a different format than the COW App Extractor format.