What clients hear
An estimate says: here is what we propose to do and for how much. An invoice says: this amount is now due for work or materials as stated.
Mixing the labels confuses non-tradies. Keep the language on the document title consistent with the document type.
Legal and practical notes (not advice)
Formal accounting or legal advice belongs with your adviser. Practically, estimates often need an expiry, and invoices need a due date and clear payment details.
GST should be transparent where it applies. Workspace tax labels help your PDFs stay consistent.
The conversion path
The cleanest story is estimate accepted, then invoice, then payment. You keep one commercial thread instead of parallel spreadsheets.