You can “call” it the informal version but they’re quite different. だ implies you believe something is true, so you can never use か　to ask a question with だ, since it makes no sense to be asking what you just stated you believed was true. です works with everything. When using だ with な-adjectives you have to drop the な.

その車の社内はきれいな。－＞　きれいだ。