Can carboxylic acids be oxidised further? I know that compounds like alcohols can be further oxidized to aldehydes (or ketones) and to carboxylic acids. But, is carboxylic acid the best oxidized form of a given compound? 
What happens when carboxylic acids further reacts with oxidizing agents like $\ce{KMnO4}$?
In carboxylic acid, the carbon atom of the COOH group is already in high oxidation state, namely +3. In order to reach a higher oxidation state (+4), it requires breaking the C—C bond, typically to form molecular CO2. Thus, oxidation of carboxylic acid in strongly oxidizing conditions is known as a decarboxylation reaction.