pub fn flatten_annotations(doc: &mut Document) -> Result<(), AnnotBuildError>Expand description
Flatten all non-widget, non-link annotations on all pages.
Reference integrity: when a markup annotation is flattened, its associated
/Popup companion annotation is removed as well, so no /Parent reference
is left dangling. Cross-annotation /IRT (reply threads) and structure-tree
OBJR references that point at a flattened annotation are NOT rewritten;
per ISO 32000-1 §7.3.10 a reference to a removed object resolves to the null
object, which conforming readers tolerate. Rewriting those references is
intentionally out of scope (tracked as a follow-up).