Answer:
What goes through a door but never goes in. And never comes out?
Two horses, swiftest traveling, harnessed in a pair, and grazing ever in places. Distant from them.
What has four legs during the day; and six or eight during the night?
Being able to interpret the letters on this screen proves that you have this quality.
It stands upright and can be quite grand. Its secret is not hidden but right at hand. What is it?
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?