Let $(M,J_{M})$ be a almost complex manifold and $(N,J_{N})$ be a complex manifold. I want to prove that $F^{*}(\mathcal{O}_{N})\subset\mathcal{O}_{M}$ implies that $F:M\rightarrow N$ is almost complex. $\mathcal{O}_{M}$ denotes the sheaf of holomorphic functions on $M$ and similarily for $\mathcal{O}_{N}$.
$F:M\rightarrow N$ is almost complex means that $dF\circ J_{M}=J_{N}\circ dF$.