Duellist's Edge (X) "A Weapon with the Duellist's Edge (X) Special Rule grants a bonus to Focus Rolls in Challenges."
In Step 3 of the Challenge Sub-Phase, the Focus Step, if a Player has declared that the Model under their control will use a Weapon with the Duellist's Edge (X) Special Rule or has the Duellist's Edge (X) Special Rule, then that Player gains a bonus equal to the value of X on the Focus Roll.
Critical Hit (X) "Attacks made with the Critical Hit (X) Special Rule have a chance to automatically cause a wound and inflict 1 extra point of Damage."
When any Hit Test is made for an attack with the Critical Hit (X) Special Rule, if the result of the Dice Roll, before any modifiers are applied, is equal to or greater than the value of X attached to this variant of the Critical Hit (X) Special Rule, then if a Hit is inflicted by that Hit Test, that Hit becomes a 'Critical Hit'.
A Critical Hit automatically inflicts a wound without any dice being rolled, counting as the roll of a '6' for any variable Special Rules that might be triggered by a Wound Test, and increases the Damage of the Hit by +1.