Polymorph spells and equipment bonus

[Guez]

Polymorph spells says that equipment merge with the form and passive bonus remains.
Let's take Dinosaur Form of a trex, heightened to 5th for example.
The spells says that you do 1d12 with the bite, plus another die for the heightened spell.
If you have a +2 weapon when you merge, you maintain the bonus to damage and hit (+2 / +2d12)?
Same thing with +2 armor, is giving bonus to the form?

[ScegfOd]

Aren't you not attacking with your sword? Didn't you just say bite attack? Why would its bonus apply?

The armor question makes sense, at least. I think it doesn't count because it's an enhancement to the armor, and you're using T-Rex hide instead of your armor when polymorphed. I could see it being ruled differently, though.

In PF1 passive bonuses were things like +2 Str or +2 Cha. They weren't bonuses that made an item itself better, but rather they made the bearer/user better. So things like a ring of protection's deflection bonus would still work since it makes some sort magic pushy-field around you, but carrying a flaming sword when not polymorphed wouldn't enable all your claws and teeth to be on fire all the time.

[Guez]

After some testing, we come across the phrase "These special statistics can be adjusted only by penalties,
circumstance bonuses, and conditional bonuses."
Almost all items don't give that type of bonus.
So you can't use that, only effect that for example make you fly or telepaty.
Statistics of the form can be altered only by druid vestments, that make you substitute your statistics with the forms one (so you can only keep you armor class, attacks, movement speed etc in the form, if yours is better)

[ScegfOd]

Your response contains the answer for the armor part your original question: item bonuses don't apply.
As for the weapon part, the spell Animal Form (and probably the other Form spells) specifies that you only use the attack given by the form.

Also, the phrase (at least in Animal Form) is "the constant abilities of your gear still function"
If you get constant Fly rather than an activated ability, then yes you would keep that. Same for every other ability...