Catalyzes the ATP- and NADPH-dependent reduction of carboxylic acids to the corresponding aldehydes (PubMed:23248280). Catalyzes the reduction of a wide range of aliphatic fatty acids (C6-C18) into their corresponding aldehydes. Can also reduce benzoate to benzaldehyde. Has a preference for NADPH over NADH as the electron donor (PubMed:23248280). a carboxylate + ATP + H(+) + NADPH = AMP + an aldehyde + diphosphate + NADP(+) Binds 1 phosphopantetheine covalently. Optimum pH is 7.5. Displays in vitro half-lives of 73, 70, and 48 hours at 26, 30, and 37 degrees Celsius, respectively, indicating it is a relatively stable enzyme. The N-terminal domain likely catalyzes substrate activation by formation of an initial acyl-AMP intermediate, the central region contains the phosphopantetheine attachment site, and the C-terminal domain catalyzes the reduction by NADPH of the intermediate thioester formed from the attack of the phosphopantetheine thiol at the carbonyl carbon of acyl-AMP (By similarity). Large-scale domain motions occur between the adenylation and thiolation states. Phosphopantetheine binding alters the orientation of a key Asp, resulting in a productive orientation of the bound nicotinamide. This ensures that further reduction of the aldehyde product does not occur (PubMed:28719588). This enzyme can be applied to the microbial production of fatty alkanes and fatty alcohols that have numerous applications as fuels, fragrances, emollients, plasticizers, thickeners, and detergents. Thus, together with complementing enzymes, the broad substrate specificity and kinetic characteristics of Car opens the road for direct and tailored enzyme-catalyzed conversion of lipids into user-ready chemical commodities. The conversion of fatty acid into aldehyde involves three key steps: adenylation of the bound fatty acid substrate to form an AMP-fatty acyl complex, formation of a thioester linkage between the fatty acyl moiety and the phosphopantetheine prosthetic group, and reduction of the thioester intermediate to the aldehyde. Belongs to the ATP-dependent AMP-binding enzyme family. Carboxylic acid reductase subfamily.