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

: Based on the name 09.2018 , this archive likely contains data, software updates, or database snapshots from September 2018 . Large public datasets, such as the Open Payments data from CMS, frequently use 7-Zip to distribute annual reporting information. How to Extract the Archive

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

: To successfully extract the content, you must have all preceding parts (e.g., 09.2018.7z.001 , .002 , .003 ) in the same folder.

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