In order to export an estimate to P6 you will be required to the Software Development Kit (SDK) installed.  Attached are selected pages from the Primavera administrator manual that addresses this. Also P6 will have to be installed in the same environment as HeavyBid. For example if you are running HeavyBid on a typical server install then P6 will also have to be on the server. SDK is free but typically is not installed as a default.

Primavera SDK Install Instructions