I don’t have much of a clue here. Never heard of anyone playing Civ IV or any PC game on a tablet. When I think of tablets I think of mobile games for iOS or Android.
However, you did not mention what kind of tablet you have. I did a search for answers and it appears that the Microsoft Surface works for PC games or other Windows based tablets. No clue if it holds up for big games or not.
Anyway, you can buy digital games now. Look for IV on sale at Steam or GOG. You can get it for around $7.
My guess is IV won’t play well with tablets mor be very touch friendly.