I would recommend not including large content in a question, as that is frequently suggestive of "Not a Real Question" or "Too Localized", and suggests that the asker might not know enough about what is happening to be asking in the first place.
That said, I can imagine that there could be cases where it would still be legitimate to do so. Maybe.
If so, and if there isn't a well-accepted, well-known-as-safe tool that would apply already (like jsfiddle.com for JavaScript/HTML/CSS problems, or Pastebin.com for more general code), what I would do is post such content on my own site, within a plain HTML page that does not require any special plugins, works well without JavaScript enabled, and is very clear about any resources that are included.
I would absolutely avoid any attachments that can seem to be dangerous. So, absolutely no exe
, zip
, or doc
files, for instance.
My goal, as someone hoping to get someone to look at my content to learn more about my problem, would be never to include that content in a way that would discourage them from doing so. Long content itself does that, as do links to pages that are unfamiliar, or have content which is perceived to potentially be dangerous.