PdfMarkInfo
data class PdfMarkInfo(val marked: Boolean = false, val userProperties: Boolean = false, val suspects: Boolean = false)
Catalog /MarkInfo dictionary (ISO 32000-1 §14.7.1).
Tells consumers whether the document carries tagging information used for accessibility (screen-reader logical reading order), structured extraction, and reflow. Tagged-PDF/A files set marked = true.
null from PdfDocument.markInfo means the document doesn't carry a /MarkInfo dict at all — i.e. it's not tagged.