Hi,
once you have created the button, you set the action as 'submit a form'. When you add this, you will be prompted to enter the URL. You need to type mailto: followed by the email address that you want the end user to send it to. For example, if your client/collegue wants the form to be sent back to them and their email address is test@test.com then you would enter
mailto:test@test.com
into the URL box. You want to make sure you select the PDF option, which will attach the whole completed form to the email.
hope that helps
Sebastian