Function parse_page_boxes 

pub fn parse_page_boxes(
    resolver: &Resolver<'_>,
    pages: &[PageInfo],
    page_index: usize,
) -> Option<PageBoxes>

Read the page-box and presentation-hint entries for a page.

pages is the document’s page list (usually PdfDocument::pages()); page_index is the 0-based page number.

The inherited MediaBox and CropBox come from PageInfo (the page-tree walker resolved inheritance at document-load time). The page-local BleedBox, TrimBox, ArtBox, UserUnit, Dur, Trans, and AA are read fresh from the page dict via the resolver.

Returns None if page_index is out of range; otherwise always returns a populated value (missing entries default per spec).