Aaron D. Campbell

This plugin allows you to list attached files on posts. It comes with a default 
icon set (by famfamfam), with icons for most major files types. You can add 
your own icons, as well as control many aspects of the file list (whether you 
want to show icons, whether to add the lists to exerpts, place them on all posts, 
show them on category pages, etc).

Attachment Manager

This will allow you to better manage how your attachments are handled.  Attachments can be easily listed after posts, complete with icons.

Zodan

martenmoolenaar

This plugin allows site admins to protect specific attachment file types (e.g. Pdf, Doc(x)) from direct access. Instead, the files are served through WordPress, allowing you to check if a user is logged in or has the required permissions before granting access.
Features: 
* Adds a checkbox to media attachments to mark them as “Authorized only”. 
* Creates an internal page and rewrite rules to intercept requests to protected file types. 
* Checks user login status (or other custom logic you add) before serving files. 
* Provides a settings page to specify which file types should be protected.
<h3>License</h3>
This plugin is licensed under GPLv2 or later.

Z Authorized Downloads

Protect documents from unauthorized download.

Attachment Manager vs Z Authorized Downloads