: The .rar extension means the contents are compressed to save space. You would need a utility like WinRAR or 7-Zip to "extract" the installer inside before you could use the software.
: Many designers keep specific archives like this because newer versions of Creative Cloud sometimes drop support for older operating systems or change workflows that users prefer in the 2019 build. Illustrator 2019.rar
The text is the filename for a compressed archive (RAR) typically containing the installation files for Adobe Illustrator CC 2019 . Illustrator 2019.rar
While it looks like a simple utility file, here is why it might be considered "interesting" or important to someone: Illustrator 2019.rar