The pad switch on a condenser microphone is there to protect the microphone's own electronics from overloading. In an emergency you can also use it if your preamp is overloading, but it's a bad long-term solution for that problem. Nearly always, the inherent noise level of the microphone is the same regardless of the switch setting--so if you engage the pad, the signal decreases by 10 dB but the noise level remains the same. So the noise increases 10 dB relative to the signal.
A much better solution (as long as the microphone isn't near its overload point due to high sound pressure levels, wind noise or inadequate powering) is to use resistive pads at the inputs of the preamp. Some preamps have a "low sensitivity" switch for this purpose, or internal jumpers. If not, then various brands of in-line resistive pads are available (they're not very expensive), which should be placed right at the inputs of the preamp, and the mike cables should then be plugged into them. They don't interfere with phantom powering, and they reduce the microphones' inherent noise to the same degree as they reduce the signals, thus preserving the signal-to-noise ratio of the recording.
--best regards