Did you download this intentionally? If it arrived as an unsolicited email attachment or appeared suddenly in your downloads folder, do not open it .
If the archive contains a file like 546565465756767.pdf.exe , it is a virus disguised as a document.
If you have confirmed the file is safe and legitimate, you need specific software to extract it, as Windows and macOS do not always support .rar natively: Use 7-Zip (Free/Open Source) or WinRAR.