Performing a Command-C copy of a PDF embedded (via the <embed> tag) in an HTML document does not work. Note also that changing focus away from the PDF (with selected text in the PDF) does not properly change color to grey. Instead, it retains the normal "active selection" color.
<rdar://problem/20639201>
Note that opening a PDF document in WebKit *does* work. It's only a problem when the PDF is hosted in an <embed> tag.