: Use 7z t 3gj8.7z to verify that the archive isn't corrupted before processing it in your workflow.
: If you can't open it, use a hex editor to see if the first few bytes are 37 7A BC AF , which confirms it's a 7z archive. 3gj8.7z
If you are trying to implement a way to handle this file in a software project, here are the standard "features" you might be looking for: : Use 7z t 3gj8