[Anhydrides react with water to form respective acid (or base). eg. $\ce{CO2}$$+$$\ce{H2O<--> H2CO3}$, $\ce{CO2}$ is anhydride of $\ce{H2CO3}$. We can find anhydride by removing water from acid(or base).]


On doubling and then removing water from $\ce{HNO4}$, I got $\ce{N2O7}$ as its anhydride but I couldn't confirm it from anywhere. Nothing was written on all the sites I went to about its anhydride.

Also, I wanted to ask whether we can find anhydride of any acid or base by removing water (doubling before if required)?