This plugin will allow you to attach a single file to multiple posts, but will also will allow you to detach any file.
<ul>
<li>Support http://xparkmedia.com/plugins/file-un-attach/</li>
<li>Languages http://xparkmedia.com/plugins/file-un-attach/#languages</li>
</ul>

File Un-Attach

This plugin will allow you to attach a single file to multiple posts, but will also will allow you to detach any file.

threadi

Filter in the media library for files that are assigned to any post type. The files must be assigned to the pages or posts for the filter to work.
The development repository is on <a href="https://github.com/threadi/media-attached-filter" rel="nofollow ugc">GitHub</a>.

Media Attached Filter

Filter in the media library for files that are assigned to any post type.

File Un-Attach vs Media Attached Filter