I have a Livecycle designer 8 form and used dynamic dropdownlist with ODBC connection. After applying usage rights to the form using acrobat professional when i open with reader my first dropdown is showing records but the dependent dropdown in blank. If i open the same form with acrobat it is working (The second dropdown is populating records according to first dropdown).
You need to enable the additional rights in your form so that Reader can also connect to the database.
And the rights needs to be elevated by LC Rights Management.
Let me just rephrase what PDFGuru said: You cannot do that by adding extended Reader rights in Adobe Acrobat Pro, you need LiveCycle server software for that. It's a common misconception that there is just one set or extended Reader rights and that one can assign all of them with Acrobat Pro.