You can add more than one signature line to a document, and in fact, it is common to do so since many files are a collaborative effort.
Rịba ama na ị nwere ike itinye ihe karịrị otu akara aka akara na akwụkwọ, na n'eziokwu, ọ bụ ihe a na-emekarị ebe ọ bụ na ọtụtụ faịlụ bụ mgbakọ aka.