C# – Access SharePoint Document Library from web application

Applying information rights management might help you achieve this. Have a look at the following link

http://office.microsoft.com/en-in/sharepoint-server-help/apply-information-rights-management-to-a-list-or-library-HA101790603.aspx

You have several ways to achieve this. The out of the box option would be using queries (from server code or ajax) your list SVC. In case you don't know, all lists have an associated service to pull information.

1. http://msdn.microsoft.com/en-us/library/hh134614(v=office.14).aspx
2. http://www.dotnetmafia.com/blogs/dotnettipoftheday/archive/2010/01/21/introduction-to-querying-lists-with-rest-and-listdata-svc-in-sharepoint-2010.aspx

There is a wonderful js library at codeplex, spservices, that helps you to query your sharepoint. With this list you could do something like this (sample code taken from codeplex samples)

<script language="javascript" type="text/javascript">

$(document).ready(function() {
  $().SPServices({
    operation: "GetListItems",
    async: false,
    listName: "Announcements",
    CAMLViewFields: "<ViewFields><FieldRef Name='Title' /></ViewFields>",
    completefunc: function (xData, Status) {
      $(xData.responseXML).SPFilterNode("z:row").each(function() {
        var liHtml = "<li>" + $(this).attr("ows_Title") + "</li>";
        $("#tasksUL").append(liHtml);
      });
    }
  });
});
</script>

More information at http://spservices.codeplex.com/wikipage?title=GetListItems? Keep in mind if the list has security restrictions you will run into pretty "interesting" authetication issues as you are running this calls outside sharepoint and it will not know who the hell is making the calls. So, just as a suggestion, consider running your pages under sharepoint.