Right-click Dan04.7z.001 and select "Extract Here". The software will automatically detect and join the other parts to recreate the original file.
To open this file and read the story, you generally need all subsequent parts (e.g., .002 , .003 , etc.) in the same folder: Dan04.7z.001
While "Dan04" does not correspond to a major mainstream title, it is a common naming convention for: Right-click Dan04
Ensure you have the full set of files starting with "Dan04.7z." Use an extraction tool: Use a program like 7-Zip or WinRAR. Dan04.7z.001
The extension .7z.001 indicates that a large file (possibly a visual novel or a collection of story-related media) was broken into smaller parts for easier uploading and downloading.