To get the document GUID value or the document size on the disk the ChronoDocument object should be used along with the get_field_value function.
The following variables must be used:
ChronoDocument.get_field_value(Guid) returns the unique identifier for the document;
ChronoDocument.get_field_value($size_in_bytes) returns the document (sum of all all pages) size in bytes, this also updates the document/page fields "DocSize" and "PageSize";