gistfile1.php

<?php

add_action( 'new_job_application', 'send_new_job_application_confirmation', 10, 2 );

function send_new_job_application_confirmation( $application_id, $job_id ) {
  $candidate_email = get_post_meta( $application_id, '_candidate_email', true );
  $message         = sprintf( "Thanks for your application for '%s'. We'll get back to you as soon as possible.", get_the_title( $job_id ) );
  $attachments = array( WP_CONTENT_DIR . '/uploads/file_to_attach.zip' ); // Direct link to a file you want to attach

  wp_mail( $candidate_email, 'Your Application on ' . get_bloginfo( 'name' ), $message, '', $attachments );
}