If you go to adobe.com take a look at the the acrobat feature sheet, in particular the one that shows the different features available in Reader vs. Acro Standard vs. Acro Pro. Basically RE enables Reader to use features available in Acrobat Standard. There are tons of features available in Acrobat Pro beyond that, but they are more typically features used by form developers rather than end users.
Sorry Aandi, got to correct you, but RE'ing a PDF can allow it to access a DB via ODBC. However, I would personally recommend you make a web service call and let the server handle hitting the DB if needed. It is much more secure, less work to set up (don't need a local ODBC connection on each client), and easier to work with IMO.
Chris
Adobe Systems