Dropdown list

I want a dropdown list with lots of pre typed options and also the ability to enter your own text.  When the user starts typing, I want it to pare down the options that match, much like if you are entering your state in a form, enter W and jsut the "w" states now show in the box.  My form does allow the user to enter text (when opened with Acrobat reader), but does not pare down the options that pertain to what they've entered.  If I don't open it in Acrobat, it will do this, however, the text the user is entering HAS to be an option, you can no longer enter your own text.  How do it get it to allow me to type my own text, while narrowing the options that have been pre-entered. but also allow my own text if the option isn't in the list?  I hope I'm making sense.  

I have auto complete set to advanced in preferences and the box "allow user to enter text" checked in properties.