Professional Edges are very special abilities that reflect many years of practicing a particular trade. In some cases they may also represent special blessings from higher powers as well.
These Edges help you create a character who is far more competent in his chosen field than most others. If you want to make a very effective Mad Scientist, for example, you could combine the Arcane Background (Weird Science) with the Gadgeteer and Mr. Fix It Edges.
Professional Edges represent many years of training so their Requirements are quite high. Players may purchase Professional Edges after character creation, but should usually lead up to it story-wise by practicing the affected trade during down-time or in between adventures. The time spent acquiring one of these abilities is subjective and up to the Game Master, but makes the game much more believable if a little narrative time is spent training.
Stacking: Bonuses to the same Trait from different Professional Edges do not stack. If you make a hero with both the Woodsman and the Thief Edges, for example, he gains +2 to his Stealth skill, not +4.
Savage Worlds Deluxe Edition p. 41