Your travel to and from Windsor Castle is included in your London Pass + Travel package. Journeys are valid from London Paddington to Windsor & Eton Central via Slough only. Show your valid London Pass to the ticket controller at London Paddington to board to train at no extra cost. https://www.londonpass.com/london-transport/travelcard-validity.html
https://www.londonpass.com/london-transport/travelcard-validity.html