Planning permission is not normally required for repairing, fitting or replacing doors and windows (including double glazing).
However, if the building is listed or is in a conservation area (or other designated area) you should consult with your local planning authority.
Also, if you are a leaseholder, you may first need to get permission from your landlord or management company.
Disclaimer - Wales
This is an introductory guide and is not a definitive source of legal information. This guidance relates to the planning regime for Wales. Policy in England may differ. If in doubt contact your Local Planning Authority.