Files with this naming convention are frequently shared on third-party forums or file-hosting sites. If you didn't get this directly from an official developer channel (like their Steam page or official crowdfunding site):
The file is the second part of a multi-volume compressed archive for an early alpha version of the game 171 . 171_pr__alpha_.part2.rar
: The "pr_alpha" naming suggests this is a Pre-Alpha or early Alpha build. These versions are typically released to backers or testers to find bugs and gather feedback on the "Pelotas" map and basic mechanics. Files with this naming convention are frequently shared