  Let $X$ be a normal complex variety and $\pi:\tilde X \to X$ a resolution of
singularities. We show that the inclusion morphism $\pi_*\Omega_{\tilde
X}^p\hookrightarrow \Omega_X^{[p]}$ is an isomorphism for $p <
\mathrm{codim}_X(X_{\mathrm{sing}})$ when $X$ has du Bois singularities, giving
an improvement on Flenner's criterion for arbitrary singularities. We also
study the $k$-du Bois definition from the perspective of holomorphic extension
and compare how different restrictions on $\mathscr H^0(\underline \Omega_X^p)$
affect the singularities of $X$, where $\underline\Omega_X^p$ is the
$p^{th}$-graded piece of the du Bois complex.
