20 db pads are common and they are interchangeable - so long as they are
designed for 50 ohms. I have seen pads for 75, 92 and 300 ohms, but they
are not common.

The pad also makes the input impedance of the device receiving the signal
more constant, and is often recommended for that reason. As was stated, be
sure to compensate for it.

73, Colin K7FM