Occasional Wife (1966)

Peter, a junior executive at a New York business, figures out that single men at his company are generally passed over in favor of married men, who the top execs think are more stable. So Peter asks his friend and upstairs neighbor, Greta, if she'd be willing to pose as his wife for company functions. She agrees, not knowing how it'd affect her personal life. And whenever someone from his company unexpectantly dropped by "their" apartment, Peter would run up the fire escape two floors to fetch Greta, much to the bemusement of their neighbor in-between.