Separate the sales size from field measurements
A familiar size description can help begin a conversation, but it should not become the final order by itself. Ask who will measure the existing opening and verify the proposed installation. Trim, finished surfaces and hardware space can affect the plan. Do not rely on a measurement copied from a neighboring home or an old estimate.
Identify whether the opening stays the same
Replacing a door within an existing opening is different from widening or raising that opening. State that intention early. Structural or surrounding building work needs its own responsible provider and applicable review. The door supplier’s product dimensions do not authorize changes to the wall or prove that the opening can safely be altered.
Review the final order as a complete item
Before approval, check the model, size, section layout, windows, finish and required performance in one place. Confirm how any retained operator will be assessed and whether new tracks are included. If the opening changes after measurement, stop and resolve the order rather than assuming an installer can trim or modify the supplied assembly to compensate.
Your questions
Is the size printed on an old invoice enough to order a new door?
It is useful background, but the installer should verify the current opening and the selected product requirements before ordering.
Can a door installation quote also cover widening the opening?
Only if the additional work is explicitly included and assigned to the appropriate provider. Do not infer structural work from a door-only price.