How to reduce rise/fall time while amplifying square pulses with op amp?
An ideal op-amp will amplify and not distort. Unfortunately op-amps are not perfect and to amplify edges you need quite a high gain-bandwidth-product (GBP). GBP tells you about the speed of the op-amp and can be found in the data sheet. Also, an op-amp has another parameter called "slew rate". This tells you how fast the op-amp output can move in volts per microsecond.

An op-amp with a slew rate of 1V/us will easily cope with a small signal but at higher levels of amplification the edges will begin to have finite ramp speeds and eventually a square wave will look more like a triangle wave.

Choose your op-amp carefully.