The .004 file extension is commonly used by a variety of file compression and archiving tools. Certain compression and archive utilities possess the ability to break archive files down into separate volumes when an archive file becomes too big. This makes it easier to distribute the files over the Web.
When a file archive is broken down into smaller parts, the volumes within the archive are given a series of extensions which are usually in sequence. The .004 file extension is normally assigned to the fourth volume of the file archive. A split archive file cannot be opened unless all of the volumes within the archive are combined.
Popular applications that can break archive files down into multiple volumes include the WinRAR application and 7-Zip archive utility.
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