Backstab is the starting ability received by Rogues at level 1 in Dragon Age RPG. The full explanation of the ability is outlined below. Highlighting the key section in bold
You can inflict extra damage with an attack if you can strike an opponent from an unexpected direction or catch them unawares. You must approach your opponent with a move action If attacking with a melee weapon. Then you must win an opposed test of your Dexterity (Stealth) vs. your target’s Perception (Seeing). If you win the test, you can use your major action this round to Backstab him. This is an attack with a +2 bonus to the attack roll that inflicts +1d6 extra damage. You cannot Backstab an enemy that you begin your turn adjacent to (but see the Bluff power at level 4.
This section differs between the printed book and the PDF edition.
The same highlighted sentence in the printed book reads:
You must approach your opponent with a move action
We are struggling to figure out whether this means that the move action is only required for melee weapons (and ranged surprise attacks are possible) or backstab is only possible with a melee weapon, the 2 books appear to imply different answers and we can’t figure out which is which.