EDIT: This doesn't work anymore
I've found out how they're disabling copying, so I'm turning my comment into an answer.
Here's the script that runs on the page that prevents copying:
function rtcScript() {
document.oncontextmenu = null;
document.onselectstart = null;
document.onmousedown = null;
document.onclick = null;
document.oncopy = null;
document.oncut = null;
var elements = document.getElementsByTagName('*');
for (var i = 0; i < elements.length; i++) {
elements[i].oncontextmenu = null;
elements[i].onselectstart = null;
elements[i].onmousedown = null;
elements[i].oncopy = null;
elements[i].oncut = null;
}
function preventShareThis() {
document.getSelection = window.getSelection = function() {
return {isCollapsed: true};
}
}
var scripts = document.getElementsByTagName('script');
for (var i = 0; i < scripts.length; i++) {
if (scripts[i].src.indexOf('w.sharethis.com') > -1) {
preventShareThis();
}
}
if (typeof Tynt != 'undefined') {
Tynt = null;
}
}
rtcScript();
setInterval(rtcScript, 2000);
Notice that it's setting every element to not be copyable, selectable, or cuttable, as well as disabling the context menus. This is trivial to bypass by disabling scripts on the page. See this question for how to do it on Chrome. I've tested this myself - if you disable JavaScript via that method while viewing the locked document, you can immediately begin selecting and copying the text with no issues.