The certificate of authenticity is a document which attests to the origin of a work of art. It usually includes information such as title, dimensions, medium, year created, and artist name. However, the artist's signature can sometimes be enough to prove authenticity.
On Artsper, you can download the certificate into your account after delivery confirmation. Some hand-signed works do not require one; in this case, the invoice will be sufficient to prove their authenticity.
All information is available on the work sheet regarding the accompanying documents.