Why did schrooge keep open his office door?

Scrooge kept his office door open to signal his willingness to conduct business, as he was primarily focused on making money and maintaining a strict work environment. The open door also allowed him to keep an eye on his underpaid clerk, Bob Cratchit, ensuring that he was working efficiently. Additionally, it served to reinforce Scrooge's isolation and lack of personal connection, as he preferred to keep interactions strictly professional.