[RPG] How many Pact Weapons can a Blade Pact Warlock create

If you transform one magic weapon into your pact weapon, every time you create your pact weapon thereafter your "bonded" weapon will appear.

Pact of the Blade (PHB p. 107-108)

You can transform one magic weapon into your pact weapon by performing a special ritual while you hold the weapon. You perform the ritual over the course of 1 hour, which can be done during a short rest. You can then dismiss the weapon, shunting it into an extradimensional space, and it appears whenever you create your pact weapon thereafter.

This is also addressed in the April 2016 official rules answers:

If a warlock uses Pact of the Blade to bond with a magic weapon, does that weapon have to be a melee weapon, and can the warlock change the weapon’s form?

You can also use Pact of the Blade to bond with a magic weapon, turning it into your pact weapon. This magic weapon doesn’t have to be a melee weapon, so you could use the feature on a +1 longbow, for instance. Once the bond is formed, the magic weapon appears whenever you call your pact weapon to you, and the intent is that you can’t change the magic weapon’s form when it appears.

You are proficient with it.

While a warlock is only proficient in "simple weapons" you can create any melee weapon and you are proficient with it. Martial weapons often are stronger and have other abilities.

An upgrade for your Mace would be a Flail or a Warhammer which all deal bludgeoning damage, but martial ones have 1d8 instead of 1d6 as damage dice and the Warhammer can be used two-handed for 1d10 as damage dice.

You can create one as action.

This means wherever you go, you are never without a weapon.

You can switch the weapon type to fit different situations (sometimes you might prefer a weapon with reach or a different damage type, keep in mind this feature is lost as you bond to a specific magic weapon).

Also you can indeed create throwing weapons, because they are basically melee weapons with aerodynamics. So while taking a whole action to recharge, you are never out of ammo.

It is magic

In early levels you might not have a magic weapon when fighting against a creature with immunities or resistances versus non-magical weapons. This weapon overcomes such resistances.

You can bond to any magic weapon as pact weapon

This is not restricted to melee weapons, and you have the weapon always ready.

Invocations

Lifedrinker and Thirsting Blade benefit you with abilities you can only use with your Pact Weapon.