More general information is provided in the VRBL: Additional Document References topic.

Elements

Use the AdditionalDocumentReference to model this information. This element is required if you attach a file.

Name (Path)	Cardinality	Description
Additional Document Reference (`Invoice/AdditionalDocumentReference`)	0..n	A group of elements providing information about additional supporting documents substantiating the claims made in the invoice.
Additional Document Reference ID (`Invoice/AdditionalDocumentReference/ID`)	1..1	An identifier of the supporting document.
Additional Document Reference Description (`Invoice/AdditionalDocumentReference/DocumentDescription`)	0..1	A description of the supporting document.
Attachment (`Invoice/AdditionalDocumentReference/Attachment`)	0..1	A group of elements providing information about an attached additional supporting document.
Attached Document (`Invoice/AdditionalDocumentReference/Attachment/ EmbeddedDocumentBinaryObject`)	0..1	An attached document embedded as binary object, sent together with the invoice.
Attached Document Mime Code (`Invoice/AdditionalDocumentReference/Attachment/ EmbeddedDocumentBinaryObject @mimeCode`)	1..1	The mime code of the attached document.
Attached Document Filename (`Invoice/AdditionalDocumentReference/Attachment/ EmbeddedDocumentBinaryObject @filename`)	1..1	The filename of the attached document.
External Reference (`Invoice/AdditionalDocumentReference/ Attachment`)	0..1	External reference.
External Document Location (`Invoice/AdditionalDocumentReference/Attachment/ ExternalReference/URI`)	1..1	The URL (Uniform Resource Locator) that identifies where the external document is located.

Example

<ubl:Invoice>
    <!-- Code omitted for clarity -->
    <cac:AdditionalDocumentReference>
        <cbc:ID>01_15_Anhang_01.pdf</cbc:ID>
        <cbc:DocumentDescription>Aufschlüsselung der einzelnen Leistungspositionen</cbc:DocumentDescription>
        <cac:Attachment>
            <cbc:EmbeddedDocumentBinaryObject mimeCode="application/pdf" filename="01_15_Anhang_01.pdf">JVBERi0xLjUNCiW1tbW1DQoxIDAgb2JqDQo8PC9UeXB...</cbc:EmbeddedDocumentBinaryObject>
        </cac:Attachment>
    </cac:AdditionalDocumentReference>
    <!-- Code omitted for clarity -->
</ubl:Invoice>