How do i fill a form from database?

Take a look here for one way to do that: Connect to Database from PDF Form - This Time Without SOAP - KHKonsulting LLC

Alternatively, you can write a server script that sets data on a submit and returns data on the submit response. This is actually how Acrobat was setup to transfer data.  You don't need the DB to be on a remote server to make this work.  Most  Windows versions have a server built-in. 

Another method is to transfer data using the IAC through an external application.

Here's a link to the programming interface for the IAC:

Acrobat DC SDK Documentation

You can't do it directly (any more). You will need to export the data from the DB to a text file or an XML in the right format and then you'll be able to import it into the form, using the importTextData or importXFAData methods.