Since .7z is a compressed format, you need software to "unzip" it. Right-click the file and select Extract All .
Once extracted, you will likely find a file named freemarker.jar . FreeMarker is a , not a standalone program for end-users. How to use Freemaker.7z
Download 7-Zip , right-click the file, and select 7-Zip > Extract Here . Since .7z is a compressed format