Ever tried to open two PDFs side-by-side in Preview? The app normally only lets you open a single copy of a document, so if you want to keep open a second copy—say, for easier footnote retrieval, or continued access to the table of contents—you would seem to be out of luck. We showed you one workaround a couple of months ago: running two copies of Preview simultaneously. Now an anonymous Hints reader as figured out an even easier solution.
The trick takes advantage of the PDF drop-down in any OS X Print dialog box. Open the PDF you'd like to see double in Preview. Then go to Preview's File menu and choose Print. From the PDF menu button in the lower left corner, choose Open PDF in Preview (not Print as PDF). Preview will open up a copy of the same PDF document you've been reading, which you can then arrange side by side with the original window. When you're done with your copy, you can just close it as you normally would.
One added benefit of this trick: the Open PDF in Preview command doesn't create a new temporary file that you'll need to clean up later.