: The .004 extension indicates this is the fourth part of the series. To successfully extract the content, you must also have parts .001 , .002 , .003 , and any subsequent parts (e.g., .005 , .006 ).
The file is a specific part of a multi-volume compressed archive created using the 7-Zip software. What this file type represents great-classics.7z.004
: The .7z portion signifies it uses the 7-Zip format, which is known for high compression ratios using the LZMA or LZMA2 algorithms . How to open it you must also have parts .001