Hi, i'm using Odoo14 CE, i add 

class dossier(models.Model):
   _inherit = 'purchase.order'
	​Proformat_fournisseur = fields.Binary(string="Proformat fournisseur", attachment=True, index=True, tracking=1, store=True)

so user can add proformat sent by the supplier in the purchase order, user should confirm the purchase, e-sign that proformat already sent by the supplier and saved in th field  "Proformat_fournisseur"

I already scanned the signature of the user, i can add it in the qweb report generated by Odoo such the purchase order report, but the signature should be on the buttom of the proformat sent by the supplier. so i can send it to him by mail later.