Neither Mayday nor Pan is "declared" they prefix a message of the relevant category.
You can declare an emergency using "mayday". You can't declare anything using pan. Which is exactly what the document says that you posted.
Also, mayday has to do with YOU. You can't declare an emergency on behalf of others. However, you can use Pan to send an "urgent message regarding safety", that being other aircrafts or people on ground. Hence, the example in my previous post with the forest fire. Or you can use Pan to tell ATC that you saw another plane crash, as another example.