Property Relationship

(PDF 2.0) Gets or sets the relationship between the PDF document component and the associated file denoted by this file specification.

public string? Relationship { get; set; }

Default value: null, which means that the relationship is not known or cannot be described using one of the other values.

Here is the list of the predefined relationships:

"Source" - this file specification is the original source material for the associated content.
"Data" - this file specification represents information used to derive a visual presentation – such as for a table or a graph.
"Alternative" - this file specification is an alternative representation of content, for example audio.
"Supplement" - this file specification represents a supplemental representation of the original source or data that may be more easily consumable. For example, a MathML version of an equation.
"EncryptedPayload" - this file specification is an encrypted payload document that should be displayed to the user if the PDF processor has the cryptographic filter needed to decrypt the document.
"FormData" - this file specification is the data associated with the PDF form.
"Schema" - this file specification is a schema definition for the associated object. For example, an XML schema associated with a metadata stream.

InvalidOperationException: This file specification is a string-based one and therefore can not have a relationship specified.
UnexpectedStructureException: The value in the internal PDF structure has an unexpected type.