How can I invite an applicant so they can access the drives to retrieve documents I want to share with them?

Only Recruitment Managers and Hiring Managers can enable the Document Exchange. Go to "Recruitment" in the left sidebar > Click on "Vacancies" > Select the vacancy > Then click  on "Applicants Pipeline" > Select the applicant > Then click on "Invite" in the "Document Exchange" section > Select the email template > Then click on "Submit".