multiple signers to one document

i want to be able to send a pdf to be filled out by one of our trades as a JSA/SWMS as they need to fill it out for each job they do. sometimes they will have another trade come on site and help them out that trade then needs to sign the JSA as well. how to i send the PDF to the 1 trade person who is responsible for the job and have other signature boxes for if another trade happens to come on site and needs to sign off as well without having to send them the form?