Writing a plugin for Notepad++
After looking closer at the main notepad++ site, I found this wiki. Looks pretty in-depth. http://sourceforge.net/apps/mediawiki/notepad-plus/index.php?title=Plugin_Development (link not working)
Here is a copy of the page from the internet archive... http://web.archive.org/web/20140328055927/http://sourceforge.net/apps/mediawiki/notepad-plus/index.php?title=Plugin_Development
Correct link : https://npp-user-manual.org/docs/plugins/
http://notepad-plus.sourceforge.net/uk/plugins-HOWTO.php Here is a site with some plugins - source included for examples http://sourceforge.net/projects/npp-plugins/files/
Make your plugin in less 10 minutes
This step-by-step tutorial on the official notepad++ website shows how to create a plug-in for the editor.