In the referenced PDF document the /Contents stream contains MarkedContent-operators, however no optional content dictionary exists; according to [the specification](https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G7.3883825):
> Null values or references to deleted objects shall be ignored. If this entry is
not present, is an empty array, or contains references only to null or deleted
objects, the membership dictionary shall have no effect on the visibility of
any content.
