"1) Vref applied to My ADC is 2.5v DC
3) reference to ADC as presently it is tied to VCC"
You are indicating 2.5V Vcc ?


" what is the conditioned signal to apply to its analog input port"
As Melt stated, use a voltage divider. Also if you do not need fast response a capacitor across the resistor from ADC in to ground is a good idea.

" convert mA to V DC. I dont want to use simply Resistor"
According to the law of Simon Ohm, there is no other way, you may be able to find some fancy chip that has the resistor inside, but there will still be a resistor. The usual problem with current measurements is common mode, that you handle by using an OP-amp with the inputs to either side of that awful resistor. The OP-amp also gives you the ability to have a lower voltage drop for your current measurement.

"tell some chip to apply accurate reference to ADC"
Search Maxim or the net for "Precision voltage reference" you can get virtually zero temp drift (not with a zener) and better than 1% voltage tolerance. Remember to relate your investment in reference to the resolution of your ADC and the noise introduced on your board and outside. Most designs can't even keep noise below the resolution of 8 bits.

Have fun,

Erik