adding hyperlink automatically ?

I found that many content posts, some links are refer to another piece of content or
some words are mentioned a corporate, those text will be hyper linked.
For example

if a post mentioned Adobe, Microsoft, it will be linked to it's own website http://www.adobe.com, http://www.microsoft.com

This process of job is done manually or automatically ?
What's that means of there are some kind of module that will change those text to a hyperlink automatically.