Usually an estimate unless contract says otherwise.

Convert quote to invoice?

Carry line items forward; note what changed.

Pro forma in the middle?

Sometimes used for import or budget approval before final invoice.

A quote proposes pricing; an invoice requests payment for delivered value.

Quotes may expire or be estimates—say so explicitly.

Carry agreed line items forward; note changes in writing.

Tax may differ between estimate and final invoice depending on jurisdiction.

Quote binding?: Usually an estimate unless contract says otherwise.
Convert quote to invoice?: Carry line items forward; note what changed.
Pro forma in the middle?: Sometimes used for import or budget approval before final invoice.