Users should only be allowed to add documents (MS Word) by creating a new one based on the the document library's content type. They should not be able to upload. This will ensure that every document in the library belongs to one of the library's content types and is based on that content type's document template.
A possible solution could be:
- Create a new document library.
- Create a new permission level by copying an existing level. Eg. Copy the contribute permissions level with the name "Contribute - Only Upload" and remove the permission to update / delete documents and any other specific permission you do not wish to give.
- Create unique permissions on that document library by breaking permission inheritance and giving users permission for "Contribute - Only Upload".
The users will now be able to just upload documents. Hope that helps!!!
I believe you want users to upload the document but the documents must used your content type. One way to do that is enable content types on the document library. Add your content type to the library, make it default and delete existing default content type from the library. All this can be done from library settings.
Ashish's permissions solution should work for you. Your other option would be to remove the capability from the ribbon. If you were looking to remove that functionality for absolutely everyone, then removing the capability may be a more robust solution.
There's a great blog post by Chris OConnor that covers how to use a custom user control to hide ribbon components: http://sharepointroot.com/2010/06/18/remove-actions-from-the-ribbon-sharepoint-2010/