Just like sharing comments, it is possible to choose to share an invoice's attachments with your accountant.
To set this up, go to your Settings > Inbound > Share with accountant.
From there, you can choose to include the attachments in the UBL of the invoice and/or append them to the PDF invoice.
Then you can choose to include (or not) the attachments from an invoice's details page.
To import an attachment, click on the import area to open up the file explorer and choose the document(s) to import (or simply drag & drop)
Check the Share box to share an attachment with your accountant (it will be included in the UBL file), uncheck the box to keep the attachment in your account only.
By checking the Append attachment box, it will be appended to the PDF invoice.
Note:
any attachment you want to share with your accountant must be added before the invoice gets archived (i.e. before accepting a purchase invoice or before sending the customer a sales invoice). Attachments added after archiving will always remain internal, therefore not visible to the accountant.