If you want to archive proposal on your own outside Proposales tool you can download any of your sent proposals. Downloading a proposal does not affect the status of the proposal.
Save as PDF
When inside the proposal simply press the Download PDF button in the right-side panel.
Once the customer has accepted the proposal a new email will be sent to them as a confirmation. In that email, there is a button that says PDF, press that one and the customer can download the PDF.