Do you not know what Adobe Reader is, what it's for? It's a PDF reader. Do you not know what PDF is and, therefore, not know whether you need a PDF reader? Here's an example of a document in PDF format:
http://www.irs.gov/pub/irs-pdf/f1040.pdf?portlet=103 PDF is a common document format. So, I would think you want to have a PDF reader installed. Adobe Reader is commonly found on new computers, which leads many users to think it's the only PDF reader, just as they may think Internet Explorer is the only web browser. But, there are other PDF readers, just as there are other web browsers.
If Adobe Reader is working alright for you, then there's no need to change to another PDF reader. I use Foxit Reader and am pleased with it.