The file is the second segment of a multi-part compressed archive. The naming convention suggests it is part of a larger dataset (likely "LL") that has been encoded or processed using Base64 . Overview of Multi-Part RAR Archives
: These files typically follow a sequence, such as .part01.rar , .part02.rar , etc. LL-B64.part02.rar
A multi-part (or multi-volume) RAR archive is a single large file split into smaller pieces to make storage and transmission easier. The file is the second segment of a
While "LL-B64" is not a standard software extension, the components provide clues to its likely purpose: such as .part01.rar