Because this file name is not recognized as standard software, if you have encountered it online, it could be a malicious file.

the file with an updated antivirus program (like Windows Defender, Malwarebytes, etc.) before attempting to open it. General Guide to .7z Files

If you have more information about where you saw this file, I can provide a more tailored answer. If you can provide more context, I can give better advice: Where did you this file? Is it a file you are trying to fix or extract ?

WinRAR or PeaZip can also handle this format. Instructions: Download and install 7-Zip. Right-click the derjrefkio.7z file. Select 7-Zip from the menu. Choose "Extract Here" or "Extract to [Folder Name]" .