You can register TinyMCE plugins using mce_external_plugins
filter:
add_filter('mce_external_plugins', 'my_tinymce_plugins');
function my_tinymce_plugins() {
$plugins_array = array(
'my-tinymce-plugin-name' => 'tinymce-plugin-url-of-js-file'
);
return $plugins_array;
}
You can add that code to functions.php file of your theme, or better in a WordPress plugin to make it theme independent.
Also, I recommend to not upload externa tinymce plugins to wp-include /wp-includes/tinymce/
folder; use a WordPress plugin or theme folder instead.
For example, I’ve made this test. I’ve created a file called editor_plugin.js with the content of the TinyMCE plugin js file. I’ve uploaded it to my theme root folder and I’ve added this code to functions.php:
add_filter('mce_external_plugins', 'my_tinymce_plugins');
function my_tinymce_plugins() {
$plugins_array = array(
'zbdo' => get_template_directory_uri().'/editor_plugin.js'
);
return $plugins_array;
}