The file name you provided ( download-cod-united-offensive-apun-kagames-part2-rar ) indicates a split archive. Here is what you need to know for a successful installation:
: If you receive a "Checksum Error" during extraction, it usually means one of the parts was corrupted during download. You may need to redownload specifically that part. Verdict download-cod-united-offensive-apun-kagames-part2-rar
: Unlike the base game, United Offensive heavily features driveable tanks and jeeps, especially in the Soviet campaign. etc.) in the same folder.
: Because this is "Part 2," the game cannot be installed or extracted with this file alone. You must have all other parts (Part 1, Part 3, etc.) in the same folder. download-cod-united-offensive-apun-kagames-part2-rar