How to remove wet latex paint from carpet

From what I have read it varies with the quality of the paint and the storage conditions,but 3-5 years is reasonable for unopened cans. Most of the evidence seems anecdotal. There always seems to be a case of someone using something 20 years old that they got for free and it lasted 30 years. There doesn't seem to be hard evidence from manufacturers saying that you will decrease service life by X number of years if stored for X number of months.I would do a test sample on something similar to your planned use, wood trim,drywall etc. Give it a day or so to see how the color match and texture looks. If it looks OK you have nothing to loose. If you buy new paint you will probable want to redo the whole wall so it will blend in. If the old paint doesn't match you'll have to redo the wall anyway

Depending on when this happened you might be able to just use water, or soap and water. Before it cures, latex paint is water soluble (so the absolute best time to clean it up is before it dries at all). I've had good luck using a couple of sponges and warm water - one to apply fresh clean water to the paint, and the other to blot up dissolved paint/water. You can continue this until the spot is gone.

If the paint is cured (i.e. the water isn't breaking it down) then there is a cleaner called "Oops!" that works well on paint, ink, tar etc on carpets. I would try some of that as I've heard it works wonders. It should be available at your local hardware store.