Anhydrides reversibly react with water to form a respective acid or base. For example, $\ce{CO2}$ is the anhydride of $\ce{H2CO3}$:

$$\ce{CO2 + H2O <=> H2CO3}.\tag{R1}$$

Acidic anhydride can be obtained by removing water from acid. $\ce{N2O7}$ appears to be the anhydride of peroxynitric acid:

$$\ce{N2O7 + H2O <=> 2 HNO4},\tag{R2}$$

but I couldn't confirm it with a reputable source. Also, can we produce the anhydride of any acid or base by removing water?

Anhydrides reversibly react with water to form a respective acid or base. For example, $\ce{CO2}$ is the anhydride of $\ce{H2CO3}$:

$$\ce{CO2 + H2O <=> H2CO3}.\tag{R1}$$

Acidic anhydride can be obtained by removing water from acid. Nitroperoxynitrate appears to be the anhydride of peroxynitric acid:

$$\ce{N2O7 + H2O <=> 2 HNO4},\tag{R2}$$

but I couldn't confirm it with a reputable source. Also, can we produce the anhydride of any acid or base by removing water?

[Anhydrides react with water to form respective acid (or base). eg.: $\ce{CO2 + H2O -> H2CO3}$.
$\ce{CO2}$ 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)?

Anhydrides reversibly react with water to form a respective acid or base. For example, $\ce{CO2}$ is the anhydride of $\ce{H2CO3}$:

$$\ce{CO2 + H2O <=> H2CO3}.\tag{R1}$$

Acidic anhydride can be obtained by removing water from acid. $\ce{N2O7}$ appears to be the anhydride of peroxynitric acid:

$$\ce{N2O7 + H2O <=> 2 HNO4},\tag{R2}$$

but I couldn't confirm it with a reputable source. Also, can we produce the anhydride of any acid or base by removing water?

[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)?

[Anhydrides react with water to form respective acid (or base). eg.: $\ce{CO2 + H2O -> H2CO3}$.
$\ce{CO2}$ 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)?