Increasing Weapon and Armor Profieciency?

[Dko]

What ways can a character increase Proficiency in Weapons and Armor?
I see a Fighter can become an Expert in Heavy armor and Legendary with Weapons. But is that all?
Can I use a skill increase to upgrade one? If so would it affect all my weapon/armor proficiency's, just a single category, or would it only effect one particular weapon or armor?

[Joey Cote]

There is no way to increase a your proficiency with armor and weapons except when your class advances say you get them. For example, a paladin gets Armored Fortitude at 7th which gives them Expert in shields and heavy armor. And at 13th they get Armor Mastery which gives them master in those and expert in light and medium armor. So no, you cannot spend a skill advance to increase those, or your perception for that matter.

Multiclassing can give your trained in armor and weapons you do not get training in from your base class. And if you multiclass into a class that gives you trained in something you are already trained in, that does not increase your proficiency to expert.

Probably good to note that if something gives you an increase to a specific rank (expert, master, legendary) such as the Iron Will feat and you gain an advance from something else that would raise that same thing to expert, they also do not stack, your still just expert.

[Edge93]

To add onto this:

Paladin eventually gets Legendary with heavy armor and shields.

Fighter Multiclass has a feat that makes you Expert with at least some weapons. This does nothing if your class also makes you Expert. Paladin may have something similar for armor.

Anyone can get Expert in their Racial weapons at 13th level by taking the appropriate Ancestry feat chain.

The Gray Maiden archetype increases your proficiency with Gray Maiden plate and shields, eventually getting Legendary.

Some multiclass archetypes have a feat that lets you become Master in a specific save, usually with the added perk of treating successes on that save as critical successes.