In this post i will show you how to restrict your web app so that .txt (whatever file extensions you want ) files can not be downloaded.
Open your web.config file and register following setting in your web.config
<system.web>
<httpHandlers>
<add verb="*" path="*.txt" type="System.Web.HttpForbiddenHandler" />
</httpHandlers>
</system.web>
For more details how to register handler in web.config check out this link
