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?
Best Answer
If you transform one magic weapon into your pact weapon, every time you create your pact weapon thereafter your "bonded" weapon will appear.
This is also addressed in the April 2016 official rules answers: