Thanks for reminding, I was just not sure which forum to post, so I cross posted.
2) Can the ADC output an DC voltage (0 to 5V) ?
No the ADC outputs nothing it is an input.
I am confused by your answer. For example, in a ideal case, If I input an 1kHz sine wave, 5Vp-p with 2.5V offset to the analog input of the Arduino,
it should read the value from 0 to 1023 level moving up and down. 0Vp-p should read 511 ~ 512.
Then if I output an PWM signal with a fixed value, 511 for example, to the DAC. The DAC should have 2.5V, right?