First off, there's no such thing as "Acrobat Reader". There's Adobe Acrobat and there's Adobe Reader.
Basically, Reader can do just that: Read PDF files and perform some very basic tasks like allow the user to fill in form fields and add some highlights. That's it.
Acrobat can be used to create PDF files from other formats, edit them in various ways, add form fields, security settings, etc.
For a more detailed summary see: http://www.adobe.com/products/acrobat/product-comparison.html
.
Visit my custom-made PDF scripts website: http://try67.blogspot.com
Contact me personally: try6767@gmail.com