You must have every part of the set (part1, part2, etc.) in the same folder . If any part is missing, the extraction will fail.
Downloaded archives from unofficial sources can contain malware or "cracked" files that pose security risks. Serios.Sam.3.BFE.part2.rar
Files with this naming convention are frequently found on third-party sharing sites or torrents rather than official storefronts like Steam or GOG. You must have every part of the set (part1, part2, etc