You cannot open or extract a .003 file by itself because it contains only a fragment of the total data. To access the contents, follow these steps: 7z.001 7z.002 7z.003 help please - SourceForge

: Specifies that this is the third part of a larger sequence (e.g., .001 , .002 , .003 ). How to Open It

Large files are often split into smaller "volumes" or "segments" for easier sharing via email, USB drives, or online downloads where file size limits exist. : Indicates the data is compressed using the 7z format.