Now I added the plugin: Markdown Extra
And add-on: ACF WordPress Wysiwyg Field
In functions.php I added:
// style editor
remove_filter( 'the_content', 'wpautop' );
remove_filter( 'the_content', 'wptexturize' );
remove_filter( 'the_excerpt', 'wpautop' );
remove_filter( 'the_excerpt', 'wptexturize' );
remove_filter( 'acf_the_content', 'wpautop' );
remove_filter( 'acf_the_content', 'wptexturize' );
// markdown support
add_filter( 'the_content', 'Markdown' );
add_filter( 'the_excerpt', 'Markdown' );
add_filter( 'acf_the_content', 'Markdown' );