<p>SE has <a href="https://stackexchange.com/legal/terms-of-service">a mechanism</a> in place to ensure it meets its legal obligations with respect to copyright. Users<sup>&dagger;</sup> aren't expected or required to determine whether other users are infringing someone else's copyright, &amp; in general we'll have neither the facts nor the legal knowledge to enable us to.</p>

<p>Now, I'm all right with us dealing with <em>flagrant</em> cases in the way @gung suggests, if we think letting them alone might tarnish the reputation of the site; but we need to draw a line before we're trying to guess whether a journal publisher gave permission for an author to place a pre-print of their paper on a department's website. In past cases (only a few) I've drawn that line after links to PDFs of whole books that obviously weren't intended to be freely distributed, but that's according to my own judgment rather than an established consensus.</p>

<p>&dagger; Including moderators. So if you're a copyright owner (or acting for the copyright owner) please don't confuse flagging content for moderator attention with formally notifying Stack Exchange of copyright infringement.</p>
