So what I'm wanting to do is be able to use the url of an attachment page for a PDF file, post that link on Facebook, and be able to customize the preview/featured image that shows up there.

I've tried adding facebook og image code to the Description section when I go in to edit the attachment file in the wordpress backend, but I can't seem to get that to work.

Is there a way to accomplish this or am I out of luck?

Thanks!