If an agreement is reached after the due diligence, then an APA or asset purchase agreement follows. This is a binding final agreement on the object and price, in which all matters necessary (within a takeover) are included. These include the negotiated representations and warranties, the price mechanism used, when the risk is transferred, etc. In short, it is the agreement with the object of buying and selling all or some of the assets of a target company.
After identifying the parties, an APA often includes a preamble. This is an introductory text that outlines the background, motives and intentions of the parties. Later, in a possible arbitration, the arbitrator will be able to use this document as a handle to get more information on the background of the agreement. Such a preamble has no further binding force, but does have an important interpretative meaning.
As an APA and an SPA generally contain the same elements, I refer you to our page on SPA for additional information.