To stop people/visitor publish their posts on your page, you can do this from facebook page settings. It is required sometime to make your page more secure from unwanted posts by others. Lets see the the steps to disable this permission from page settings. Follow below steps:
- Go to your facebook page
- Go to left sidebar on bottom
- Click on "Settings"
- Click on "Visitor Posts" option
- Click on "Disable posts by other people on the Page" option
- Click Save Changes