I am planning to use separate Vref with ADC.
My question, is should I bypass the Vref+ or not. The Vref will be taken separate from another circuit with jumper wires less than a feet together with ADC which I want to check.

 

Yes, absolutely add bypass, both at the ref source and at the PIC.

A bit of series impedance isn't a bad idea either, say 100 ohms to give the cap something to break against.

And your oscilloscope will be your friend here for design validation.

 

OK...a 100nf as the Vref+ to bypass it.
I am not sure why a 100R series with the Vref+
Can you explain why.

 

It gives the cap something to work against, so the noise stays on the ref side and not on the pic side.

 

100R at the Vref+ input side and a 100nf at the Vref+ pin of the PIC