Because this is a multi-part archive, you cannot open part .004 on its own. Follow these steps to access the guide:
Use The Unarchiver or similar tools that support multi-volume 7z files. a1029.7z.004
If you are missing part .001, .002, or .003, you will likely get an error saying the archive is corrupted or the "file is not a supported archive". Because this is a multi-part archive, you cannot open part
Do you have of the archive, or are you still looking for the first few files ? Because this is a multi-part archive