A file with the R00 file extension is a WinRAR Split Compressed Archive file. This file type is normally accompanied by files with the extension .R01, .R02, .R03, etc.

These split archive files are often created for convenience, so that you can download a large file over the Internet without having to download the entire file at once. You can simply download each part separately.

Splitting files like this is also useful for storing a large archive on a disk, for example. For example, if your storage device can only hold 700 MB, but your archive is five times that size, you can split it into five parts and store each part on a separate disk.

You can open R00 files with almost any program that supports RAR files, including the free PeaZip utility and several other free zip/unzip programs.