On the policy it has a different square footage than on the paper works when I bought the house (it's less), i was wondering if this is a big deal as it is a 25 square foot difference…where do they get the information? thanks!

Several ways – either you tell them, or they go to your property tax website (more accurate than you telling them) and see what the legal dimensions are, or they go out in person and measure and inspect.

Go outside and measure the outside of your house. If you're underinsured, it will be a BIG DEAL if you have a claim and can't get enough to fix your house. If you're overinsured, you're paying too much.