There is a facility using an OLE/DB connection from the form (running on Windows) to attach the DB to get data to populate the fields. I do not recommend doing this as you will need to set up and configure a Data Set Name (DSN)on each machine that will access the DB. If the DSN is not there then th ecommention cannot be made. This tends to become a maintainance nightmare as users do not understand how to set these up so IT Staff ends up having to do it.
The way to do this,without having to do anything on the client,is to set up a Web Service call that will get the data from the DB and deliver it to the client (when the button is pressed of course). If you have LiveCycle this is easily created. If you do not then most people will build a sevlet or a .Net app to do this. Then the form calls the Web Service and no configuration on the client is required.