7z is a form of file compression, much like zip or rar but different. A program is required to decompress the file and extract what is inside. Changing the file itself (the outer wrapper) to .package will not work. The reason a file has a generic white paper icon is that your operating system does not yet know which program to associate it with.
This is the program that many us use on Windows, it is free and open sourced. But let us know if you are on a Mac, because then of course different tools are required.
https://www.7-zip.org