I was having the same PDF preview issue mentioned in other posts. I downloaded the recommended .dll file but it didn’t solve the problem. When the newest beta (029) came out, I downloaded it on top of my existing Scrivener installation, but the problem persisted. Yesterday, I uninstalled Scrivener entirely, and then reinstalled the newest beta. Problem solved. PDF’s can now be previewed. Just thought I’d mention it in case anybody else was having persistent PDF preview problems.