Many job applications ask applicants to write a little bit about their work experience, why they’d be a good fit for a job, etc., in prose form. What kind of business document is the best format for this task?

A cover letter is the best format for this task. A cover letter allows applicants to introduce themselves, highlight their qualifications and experience, and explain why they would be a good fit for the job in a more narrative and personalized way than a resume or application form. It also gives applicants the opportunity to showcase their writing skills and demonstrate their interest in and enthusiasm for the position.