Good photos door and measurements make it much easier for an installer or inspector to tell whether the project is simple replacement or something more involved.
The safest approach is to confirm the city side and the neighborhood side before any demolition starts.
A few warning signs tell you the job is probably bigger than expected: rotted framing, cracked stucco or brick around the opening, windows that no longer fit square, or prior modifications that do not match the house.
For Dallas homeowners, the cleanest rule of thumb is this: if the project changes the opening, the structure, or the exterior appearance in a regulated area, assume a permit or approval may be required until verified otherwise.
If you are planning a replacement in Dallas, treat the permit check as part of the project, not an afterthought.