In Mavericks, when you QuickLook files, there’s an Open In button at the upper right, which lets you open the previewed document in the default app associated with the file in question.

But what if you want to open the document in a different app? For example, you’re previewing a Microsoft Word document, but would prefer to open the file in Preview instead.

Just click and hold on the Open In Microsoft Word button, and a list of other, compatible apps appears. Choose the one you’re after, and you’re good to go.

Source: Mac OSX Hints