Users with Shared folder , how to prevent adding new files.

hi

i have a shared folders in my server and a lot of domains use their computers to access the shared folders, some times some users changed the content of the changed folders the contents almost Word Files .

so how to prevent them from adding new files and folders in the shared folder without stop the editing in files.

i tried to change the security for the folders its good but after that they cannot save the new edit with the file,.

please help