replaced front brake pads but the pedal is still flooring

Sounds like the master cylinder. However, check the brake booster, brake lines, grommets around the master cylinder as well just to make sure those aren't adding to things with small leaks. If the fluid level stays at full, then replace the master cylinder.

By the way, does the pedal go slowly to the floor or quickly?

Brake fluid is only good for 2-3 years, after which your system corrodes. Steel cylinders have BIG problems with old DOT3/4 fluid. If your pedal is going to the floor, the most likely problem is the master cylinder. If you replace it yourself, be sure to bench bleed it before the install. If you've done brake work and had the hydraulic system open, or if you tried to vacuum bleed it at the wheel, or if you released the pedal too rapidly while bleeding, you likely introduced air into the system. I've found a gentle pressure bleed (3-5 psi on reservoir) with a check valve on the wheel bleeder works every time but not everyone has the equipment for this.