How do I fit a function inside an opening and closing do_shortcode

This should work assuming your trying to pass the URL to the PDF short code

$file= get_post_meta( $post->ID, 'teacher-resume-upload' ); 
if ( $file) { 
   foreach ( $file as $attachment_id ) { 
       $full_size = wp_get_attachment_url( $attachment_id ); 
       echo do_shortcode( '[pdf]' . $full_size . '[/pdf]' );
    }  
}