Take a Letter, Darling (1942)

Tom Verney (Fred MacMurray) is a struggling painter who accepts a job as the secretary to A.M. MacGregor (Rosalind Russell), a demanding advertising executive. Tom quickly realizes he's responsible for more than just mailing letters; he's also expected to escort Russell and her friends to parties and restaurants in an effort to shield them from unsavory advances. As they work hard to secure a lucrative tobacco account, their platonic relationship threatens to turn into something more.