Agree filling, joint preparation and the painting boundary. A primed replacement can still need final decoration after fitting. Window glazing, specialist seals and rated-door certification are outside the task even where the new architrave sits beside those systems.
Measure both sides and the top and identify whether one face or both are included. A doorway may have different trim on each side. The quote should describe the actual surround instead of assuming one opening means every adjacent decorative surface.
Top corners and returns need appropriate ordinary cutting and fitting. Show any unusual junctions before ordering material. A compatible profile and adequate lengths matter; filling large mismatches is not equivalent to a properly planned replacement surround.
Replace the accepted ordinary decorative surround with suitable joints and fixings, leaving the agreed preparation for finishing. Scope limits: Ordinary decorative surrounds only. No structural jamb or opening modifications, specialist glazing, fire-door certification or hazardous-material disturbance.