To migrate from Bind to PowerDNS you have to convert and import the Bind zone files into the PowerDNS database. Together with the PowerDNS package the program
zone2sql is installed.
zone2sql parses the Bind config and zone files in to a SQL format which can be imported into your database.
In this example I will convert the Bind zones to a MySQL dump, but
zone2sql can also be used to convert the zones to an Oracle or PostgreSQL sql file. I assume you already setup PowerDNS with the MySQL backend as published here.