My dad has little knowledge of how to use OS X, and most of the time he can't retain any knowledge of what I tell him when he asks how to do things. In a timeframe of about an hour when I wasn't using the Mac today, my dad was. When he finished and I opened my account, I noticed that Preview in the dock had been replaced with the obligatory question mark representing a missing/deleted application. I knew that my dad also had Preview in his dock, so I opened his account and there wasn't even the 'question mark', let alone the Preview icon or any indication that he had ever used Preview. I'm under the impression that he thought that dragging an app from the Applications folder to the trash did the same as dragging it from the dock - that it removes it from view, but it's still on the computer; I don't think he realises that this is actually how you uninstall apps in OS X. So is there any way that I can reinstall Preview?