You will need a file archiver tool. The most common and recommended tool is 7-Zip (free, open-source).
If you are asking how to open a 7z file in general, it is a high-compression file format. Here is how to handle it: derjrefkio.7z
Based on a search of available information, there is no direct, recognized, or legitimate software, document, or archive named "derjrefkio.7z" known to public records. You will need a file archiver tool
the file with an updated antivirus program (like Windows Defender, Malwarebytes, etc.) before attempting to open it. General Guide to .7z Files there is no direct
The name appears to be either a heavily obfuscated file, a typo, or a niche, non-public archive. ⚠️ Security Warning
download or open the file unless you are absolutely certain of the source.