Unfortunately this workaround doesn't work well for me. We're a monthly service business but our invoices change some from month to month depending on what services were actually provided.  The best way for us to do this is to duplicate last month's invoice, modify it, get it approved internally, then send it.  But you can't duplicate an invoice into an Estimate, so as soon as you duplicate, it looks like a live invoice, and begins aging.

Truly absurd that draft invoices don't exist.  A chat support agent told me last week that it sounds like a "great idea," and I said, "I know, it's such a great idea it's almost impossible to believe the market leader in web-based accounting software doesn't have it!"  She told me to suggest it to Feedback... of course.