In the world of online trading (specifically for MetaTrader 4 or 5), "Mercurial" is a common name for custom technical indicators or automated trading robots (Expert Advisors). .ex4 , .mq4 , .ex5 , or .mq5 files.
If you are a developer, this is likely a backup or a bundle of a code repository managed by (a distributed version control system similar to Git). Mercurial.rar
Always run a scan with a tool like Check Point or your preferred antivirus before opening files from unknown sources. In the world of online trading (specifically for