Can I upload a form I signed elsewhere?
No. The payment processor accepts an attestation only through its own systems, which is what the button in Seayora does. There is nowhere to upload a signed PDF, and a copy signed outside will not register.
From the guide Your Annual PCI Attestation.
Why yours is the short form
SAQ A is the shortest version of the questionnaire, and it applies to businesses that never handle card data on their own systems. That is exactly your situation on Seayora: a card number is typed into the payment processor’s own secure field, which sends it straight to the processor. Seayora never sees it and never stores it, and neither do you.
Read the whole guide: Your Annual PCI Attestation