ISO/IEC 29500-2:2021 states that “Core properties enable users to get and set well-known and common sets of property metadata within packages”. The core properties are the category of the Package, the status of the content, the resource creation date, the creator, a description of the content, an identifier, a set of keywords, the language of the content, the last modifier, date and time of the last printing, modification date, revision, subject (or topic) of the content, a title, and the version. These properties can be empty or omitted. The entire Core Properties Part can be omitted if there are no core properties present.
Thumbnails are images that are to be used to help end-users identify Parts of a Package or a Package as a whole, as stated in ISO/IEC 29500-2:2021, 12.
Digital signatures can be used to enable consumers to validate the integrity of the contents as stated in ISO/IEC 29500-2:202121, 13.