By default TinyMce should load plugins from the same folder or source that it loaded that main tinymce script from.

So you can add textpattern to /lib/wysiwyg_custom.php (or equivalent):

plugins: "table,fullscreen,paste,media,lists,charmap,textcolor,link,anchor,hr,paste,image,code,codesample,textpattern",

And then it will automatically load it from https://cdnjs.cloudflare.com/.

Or if you're using the Offline Mode plugin you can add the plugin URL to /plugins/offlineMode/offlineResourceList.txt and then click Admin > Plugins > Offline Mode > Update Offline Resources, and it will cache and use a local copy for you.

Hope that helps!  Let me know any other questions.

I am particularly interested in the textpattern plugin for pasting Markdown directly into the editor. If it is not included in the current downloaded version how do I add "https://cdnjs.cloudflare.com/ajax/libs/tinymce/4.9.11/plugins/textpattern/plugin.min.js" 

Are there any plans to update to a more modern version of TinyMCE, either 6 or 7? The documentation for 4.x has been removed from their website, and 5 hit EOL in April 2023.