Changing email “From” address

The ‘woocommerce_email_settings’ filter is what you need.

function prefix_change_from_email( $args ) {    
    global $wpo_wcpdf;
    for( $i = 0; $i < sizeof( $args ); $i++ ) {
        if( 'woocommerce_email_from_address' == $args[ $i ]['id'] ) {
            $args[ $i ]['default'] = $wpo_wcpdf->billing_email();
            return $args;
        }
    }       
    return $args; // just in case
}
add_filter( 'woocommerce_email_settings', 'prefix_change_from_email', 15 );