This question already has an answer here:
Pact of the Blade says that
You can transform one magic weapon into your pact weapon by performing a special ritual while you hold the weapon.
It doesn't specify the need for attunement. Though since the ritual takes one hour, the side-effect is that you'll attune the weapon anyway.
but, assuming there is a scenario where you're not attuned to an attunement weapon, can you still bind it as a pact weapon? I assume you won't gain its additional magic benefits beyond the +x to attack and damage rolls
secondary question: If this is possible, does that mean you won't be cursed either due to not attuning?