I'm really new to Sharepoint development and I've been asked to integrate some features into a Sharepoint site. Some files will be signed / encrypted using a 3rd party server.

I need to have some way of overriding the default behaviour of the drop-down menus displayed in file operations so that I can add a "sign" or "encrypt" menu item in them for files that can be signed or encrypted. I need that menu item to appear by default when the user creates a new document library, so I have to override the default document library.

I would be very grateful if anyone could give me a few pointers on the different operations involved in that. I've found loads of informations on webparts and I know how to create them and deply them. The same goes for custom types.

I couldn't find something that tells me how to override the default behaviour.

Any help would be greatly appreciated, cheers,