Google Contacts, the address book built into Gmail, lets you keep track of all your contacts, see when you last interacted with them, and more.
Combine report pages in order and link the finished PDF to its request.
Your report or invoice packet is ready on the same spreadsheet row as the source PDFs, with its pages in the order you chose.
Combine report PDFs in the requested order for review.
Your reports or invoices become a single PDF in your shared folder, with a link on the request you submitted.