If "P03.7z" refers to a specific dataset or archive (such as a "Part 03" or a specific "Project 03" file), you can verify its contents safely using the official , which provides details on the compression method and encryption used.
Most notably, a recent deep dive into by researchers and tech bloggers addresses a reported (and later debunked) remote code execution vulnerability in the 7z format. Key Insights on 7-Zip Security & Performance P03.7z
7z code is a part of 7-Zip program distributed under the GNU LGPL. You can download 7-Zip sources and binaries from Download Page. Does 7z compress better than zip? - Microsoft Community Hub If "P03