An invoice may contain a supportive document as information.

Examples of such documents may be a readable version of the invoice itself, work reports, certificates or other documents that relate to the purchase or the invoiced items.

A supportive document can be attached to the invoice in two ways: by providing a direct hyperlink through which the document can be downloaded or by embedding the document into the invoice.

When attaching a document using an URI, the hyperlink must point directly to the file that is to be downloaded.

An embedded document is contained in the invoice as a binary object using base64 encoding and be supplemented with information about the name of the document file and a mime code indicating the type of the file.
This allows the receiver to convert the binary code into a file that has the same name as the original file and allows him to associate the received file to a suitable application for viewing its content.
The set of allowed codes for the file type (mime code) is limited to types that can be opened with applications that are commonly used and available.

Not all country specific formats support the provision of attachments.

Elements

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

In CIUS-FR for the Supporting Document Type Code following codes are allowed:

Code	Description
`FR:RIB`	For a bank account statement (containing the IBAN/account number + account holder's name)
`FR:LISIBLE`	For the complete legible representation of the invoice.
`FR:FEUILLE_DE_STYLE`	For the style sheet used to create a legible representation.
`FR:PJA`	For an additional attachment.
`FR:BORDEREAU_SUIVI`	For a tracking slip.
`FR:DOCUMENT_ANNEXE`	For an annex document.
`FR:BON_LIVRAISON`	A delivery note.
`FR:BON_COMMANDE`	For a purchase order.
`FR:BORDEREAU_SUIVI_VALIDATION`	For a tracking and validation slip.
`FR:ETAT_ACOMPTE`	For a down payment statement.
`FR:FACTURE_PAIEMENT_DIRECT`	For a subcontractor invoice to be paid directly.

Only one additional document reference cac:AdditionalDocumentReference containing the Supporting Document Type Code FR:LISIBLE is allowed.

In CIUS-FR for the Mime Type Code, the following codes are allowed:

Code
`application/pdf`
`image/png`
`image/jpeg`
`text/csv`
`application/vnd.openxmlformats-officedocument.spreadsheetml.sheet`
`application/vnd.oasis.opendocument.spreadsheet`

Example

<Invoice>
    <!-- code omitted for clarity -->
    <cac:AdditionalDocumentReference>
        <ID>100001D</ID>
        <DocumentTypeCode>FR:BORDEREAU_SUIVI_VALIDATION</DocumentTypeCode>
        <cac:Attachment>
            <EmbeddedDocumentBinaryObject mimeCode="text/csv" filename="aaabbbccc.csv">m9iZXJ0IFMuIHdhcyBoZXJlCg==</EmbeddedDocumentBinaryObject>
            <cac:ExternalReference>
                <URI>http://www.example.com/aaabbbccc.csv</URI>
            </cac:ExternalReference>
        </cac:Attachment>
    </cac:AdditionalDocumentReference>    
    <!-- code omitted for clarity -->
</Invoice>