Design request: Phineas and Ferb invitations

[casjen]

I am new to this board, linked here from another Disser. So please let me know if this is right to ask or not. My ds is turning 7 and wants a Phineas and Ferb party. I am thinking of doing a secret agent party with the P and F theme. Is there a way to make an invitation that is generic but has P and F on it? He is enamored with Perry, so if Perry were on there too that would be amazing. I am not sure how this works, but I assume I would print the design and then fill it in right?

I just need something like "Sneak on over for a super secret birthday party!". Then, I'd need a line for date, address, time, and rsvp too.

Thanks, and again, if this is incorrect, please let me know.