Open two views of the same PDF Is there a way to open two views of the same PDF in Preview (without creating two copies of the file), or perhaps split the window and show two different pages at the same time?

This is very useful when reading a paper which refers back to equations on previous pages.
Open the first one regularly and then use the open command with the -n option.

Open Terminal
Type open -n and drop the file into the Terminal window. The full path of the file will appear after what you've typed.
Hit enter.

The -n option opens a new instance of the application (in this case the default one, as no other is specified) even if one is already running.