If you are unable to open the archive, here is the most likely reality:

Do you know the or source where this file was posted?

Use MultiPar or QuickPar to process these files. 🔑 2. Password or "Proof" Paper

Uses Reed-Solomon error correction to reconstruct missing data.

These are usually uploaded alongside the .rar files by the original poster. Check the same source (forum, Usenet group, or cloud drive) where you found the RAR.