The online-billing-service.com application has the facility to add default attachments to any type of document. It is very important to know that is accepted only the pdf format.

By accessing 'Configurations', then 'Document Layout', you can use the feature at the bottom of the page:

For each document type and each language you can define default values; for both annexes - the prepend and append.

Attachments can also be added directly from the document form. Click here to see how, as well an example of what such an annex added to an invoice looks like.