09.2018.7z.004 -

: The .004 extension indicates this is exactly the fourth segment in a sequence.

The file is the fourth part of a split compressed archive created using 7-Zip . This format is typically used to break down extremely large files—sometimes up to 16 billion GB—into manageable segments for easier sharing or downloading. Understanding Your File 09.2018.7z.004

You cannot "open" part .004 directly; you must initiate the process from the first file. 09.2018.7z.004