Google Drive is Google's file sync app that lets you store all of your files online alongside your Google Docs documents, and keep them synced with all of your devices.
Combine project PDFs in manifest order and send the owner a link.
Get PDFs merged in the order you list. The folder owner gets a link in chat. You choose where the finished file goes.
Attach one ordered PDF packet to the project task.
Your reviewer gets a single PDF in the order you set, with the finished packet attached and linked on the project task.