Ability to add PDF attachments to orders in ShipStation

Hi! We operate multiple ecommerce sites but also have retailers placing direct orders through quickbooks. We generate PDF invoices to print and then manually create labels in shipstation. It would be great if the developers could enable a way to attach PDFs (or other files types) to individual orders in shipstation. So if a team member is working remotely and generating invoices and manual labels, team members printing out the labels could also print the accompanying invoices. Thank you