The .rar extension indicates that the file is in the RAR archive format, which is used for compressing and archiving files. The .part04 suggests that this is the fourth part of a set of files that are meant to be combined.
You'll need software capable of extracting RAR files. WinRAR is a popular choice for Windows users, while 7-Zip can also handle RAR files among many others. FC2PPV-3259498-2.part04.rar
These are archives that have been split into multiple files. This is often done to make the archive easier to transfer or store on media with size limitations. FC2PPV-3259498-2.part04.rar