I’ve a free WordPress (xxx.wordpress.com) blog and now I want to install a plugin like the way I install them with my WordPress site at my own domain. Can’t find it in the menu. Isn’t this possible with a free WordPress site?
How to install a plugin for a free WordPress site?
No, you can’t add plugin’s to WordPress.com the Free websites. They can’t allow free sites to add possible vulnerable plug-ins to the server. This would drive up the costs and make it impossible to offer them for free.
The most simple answer is, no. Unfortunately not. Unless you are part of The VIP program on WordPress.com for high-traffic and high-profile sites which allows you to run custom themes, custom PHP code, ad code, and WordPress plugins.
Source: http://en.support.wordpress.com/com-vs-org/