It could be an archive of technical specifications related to telecommunications or electronic hardware testing.
Use a service like VirusTotal to upload the file (if it's small enough) and check it against multiple antivirus engines. 51991.rar
Use a tool like 7-Zip to "Open Archive" without extracting. This allows you to see the names and sizes of the files inside without running them. It could be an archive of technical specifications
English
Česky