saw a 5 lb carp in my one acre pond - I do not think there are many, if any, more. Leave him be or take him out?

What kind of carp? Common, White amur?

IMO I would remove it. My rationale is this:

To me, that 5 pound carp is not an asset to the pond. It will make the water turbid, up root plants, etc. I remove any fish in my pond I don't consider an asset. Every pond has only so much carrying capacity. Just to pick some numbers let's say the capacity of your 1 acre is 300 pounds. Do you want to tie up 5 pounds of that precious capacity in a carp?

Just my 1 cent...

If it is a grass carp, and you have massive coontail, leave it. If it's a common carp, take it out.

Yep! I made the assumption it was a common carp as it just appeared and was not intentionally stocked. If it is a grass carp and you have unwanted coontail, that makes it an asset to me and I would also keep it.

I have no clue - just floating in my boat in very clear water and saw him - my guess is common as nobody has stocked them to my knowledge -

If it is common carp, pressure cooked, they taste about like canned tuna to me.

If it is common carp, you should be able to catch it out using a bread ball, wheaties cereal ball, or dough ball fished on or just off the bottom on a small hook, about a #2 or #4. Let it run with the bait a good bit before you set the hook. I have caught lots of carp that way.