Option To Purchase Real Estate Form Real Estate "option To Purchase" Contract?

Real estate "option to purchase" contract? - option to purchase real estate form

I am interested in buying a house here in Los Angeles, CA.
Because nobody cares now, I want the guaranteed purchase option, such as 6 months. The seller wants me to sell but I would only reach an agreement that can be purchased at a fixed price within a specified time.
I have a form that is simple, said that the previous option, but legally it is? Someone else can plunge and buy the first, although I this signature of the seller?
If it is legal, you must also obtain notarized or registered with the city to be binding?