If you are currently working on this file, here is the standard process used in similar challenges:
Based on the filename , this appears to be a reference to a Capture The Flag (CTF) or digital forensics challenge. In these contexts, "write-ups" explain how to extract hidden data or solve puzzles within the file. cats 3.rar
Knowing the source will help in providing the exact flag or solution steps. Appendix:Australian English military slang - Wiktionary If you are currently working on this file,
Searching the binary data of the file for readable text. cats 3.rar