If I want to convert an .rar file to readable or viewable file, what other file is considered readable without having to decode it or something?

A RAR file is an archive similar to ZIP, so you cannot convert it, but unarchieve it with WinRAR archiver, a powerful tool to process RAR and ZIP files (http://www.rarlab.com/)

if i want to convert an .rar file to readable or viewable file, what other file is considered readable without having to decode it or something?

A rar file is a file that holds other files within it. Like a .zip file.

If you look for winrar, that will allow you to extract the files in it