The document provides a 6 step process to develop a WordPress plugin:
1. Create a folder for the plugin within the wp-content/plugins directory and add a PHP file.
2. Add plugin header information to the PHP file like name, description, and version.
3. Include code for the plugin functionality, in this case a function to limit post content length.
4. Activate the plugin from the WordPress admin plugins page.
5. Use the plugin by calling its functions, such as echoing the limited content function.
6. The plugin is now developed and ready to output customized content.