One moment — loading the bits that read and write PDFs.
Change anything, then Save. + Another adds one more; a label tells them apart.
Saved to this page only, and reachable from your phone and your computer. Nothing is uploaded to the document — these are just the values the stamps carry.
Your details and signature are stored with this page, so a signature you draw on your Mac is on your phone too. The documents themselves are opened and written entirely on your device — they are never uploaded anywhere.