Attaching documents to Approval workflow

I'm working to bring our Purchase Order Request process into Smartsheet. Have set up a workflow that goes to four different departments for approve/decline then on to accounting for assignment of the PO number. The workflow is working great but I need to attach the required documents to the Approval/Decline for each Approver. The submission for a PO Req is done via Forms. I've seen in this community where it can be done but have not been able to figure it out. Help please....Thanks!