Ok, if you have LiveCycle Forms at your disposal then that is great. You can flatten the form by having a submit button on the form that submits via HTTP to a server side component (ie: servlet) that uses the Forms API to flatten it (use renderForm() with the "PDF" transformation). You may actually want to take the data submitted and merge into another similar template that doesn't have extra objects that you wouldn't want on a flat PDF (ie: buttons).
At that point you could send the flattened PDF back to the client machine (or not if you don't want to). You couldn't send it back to the client and have it automatically send the email from the client because a flattened PDF is basically just a piece of paper on the screen and you can't run any scripts on it to give it any intelligence.
So, what you could do, is submit to the server, use Forms to create a flattened PDF, and then email that from the server (if your using Java you could use the JavaMail API to accomplish that). Or if the email must be sent from the client, and the PDF must be flattened, the only way I could see that happened would be the manual workflow and rendering the flattened PDF back to the client and then having them save the PDF and send an email with it attached.
Hope that helps.
Chris
Adobe Enterprise Developer Support