The Warlock can bond with a magical weapon to have it counted as a Pact weapon, which when not in use is shunted into an extra-dimensional pocket for retrieval at a later time. The regular pact weapon is just created out of nowhere and can take any (conventional) form.
Does this mean that a Warlock can have a bonded weapon stowed away but still create a different pact weapon if it would suit the situation better?
As an example: could you have a magical dagger stored in the pocket dimension, but summon it as a warhammer for fighting an enemy vulnerable to bludgeoning damage?