Modify Submit button to pick up data fromLiveCycle form field

[#1]

When a user clicks on “Submit by Email” button, I would like to have at “Outlook subject” filled out using

Project number “data field on the form.(Project Number : 123)

How do I modify the “Submit by Email” button on a LiveCycle form?

Thanks, you so much

My Product Information:
Live Cycle Designer, Windows

[#2]

You can use variables to fill parameters of the mailDoc method with data from from fields.

var cTo = Textfield1.rawValue,
    cSub = "Put in your mail subject here...",
    cMsg = "Put in your mail message here...\n\nKind regards\n"; // \n is for line breaks
event.target.mailDoc({
bUI: false,
    cTo: cTo,
    cSubject: cSub,
    cMsg: cMsg,
    cSubmitAs: "PDF"
});