Check the stated file size on the download page. If the downloaded file is significantly smaller (e.g., only a few KBs), it might be a corrupted download or a malicious downloader executable.
The "official" tool for this format. It offers robust repair features if the archive is slightly damaged. Download ADKSP rar
Always download ADKSP archives from official repositories, verified developer forums, or known mirrors. Avoid clicking on suspicious "Direct Download" buttons on pop-up-heavy sites. Check the stated file size on the download page