I've bought some digital books, and I was supplied with both the PDF and the mobi format.
Adding them to Calibre, they are treated as different books, and strangely they also have different metadata (the PDF versions miss publisher and author information).

Is there a standard way to tell Calibre that they are the same book? Sure I could use it to manually convert one into the other one, but I would rather keep the original one in both formats.
