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.
Deliver the current proof for your review with a decision deadline.
Your reviewer gets the current proof and a clear decision deadline by email when a card is ready for review.
Log your decision against the PDF proof you checked.
Your proof tasks show who decided, which file version they reviewed, and who takes the next step.