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.

tamlyn

Unattach is a very simple plugin which allows detaching images and other media from WordPress posts, pages and other content types.
As of WordPress 4.2 this functionality is built in. For previous versions, the only way to detach a media item from a post is to delete either the post or the media item. This plugin solves that by adding an ‘Unattach’ link below each media file in the Media Library admin list view.
<a href="http://outlandish.com/blog/2011/03/unattach/" rel="nofollow ugc">Plugin by Outlandish</a>

Unattach

Allows detaching images and other media from posts, pages and other content types.

File Un-Attach vs Unattach