Low brake pedal ?

My wife took our 2004 Impala to an appointment. When she got to the parking lot she pulled in to a space put her foot on the brake and the pedal went almost to the floor , but the car stopped.I went and checked it out, could drive the car around the parking lot and apply brakes car would stop but pedal would be almost on the floor.Car has new rotors and brake pads all the way around(less than a year old) and brake fluid is at full mark. Car does not have ABS , I don't think. What do I need to check and in what order

I know you said the brake fluid level is full, but the first thing I would check would be all the brake lines front to rear for any leaks. If all are ok, it's possibe the master cylinder crapped out, leaking past internal seals.

If I have to replace master cylinder, any special procedures that need to be taken.

Like gmtech1 says but also make sure you bench bleed that new master cyl before installing it.

My wife took our 2004 Impala to an appointment. When she got to the parking lot she pulled in to a space put her foot on the brake and the pedal went almost to the floor , but the car stopped.I went and checked it out, could drive the car around the parking lot and apply brakes car would stop but pedal would be almost on the floor.Car has new rotors and brake pads all the way around(less than a year old) and brake fluid is at full mark. Car does not have ABS , I don't think. What do I need to check and in what order

if the brake pedal goes to the floor and you see that the brake fluid is at the exact same spot when it was working then this would be the master cyl. this is usually from bad fluid being added. fluid with oil/mineral oils in it.

however I would first check for leaks. even a very small leak will do this .use a good light and check all the brake lines for any wet areas.

you have ABS unless this was some cop car or it was disabled..