Organizations, movements, and advocacy groups sometimes give away books to people interested ('sign up for our mailing list to get a free guide to...' or 'a free physical copy of ...')

Has anyone seen studies/evidence/accounts of: How many people actually read (significant shares) of the books given away in this context?

My ~30 minute search on Elicit.org didn’t find much relevant; most stuff related to literacy programs, largely for children. Also searched for accounts of ‘shares of e-books read’ but I could only find one slightly-relevant study reported by Kobo e-readers (https://www.google.com/search?q=Kobo%27s+%22Reading+Habits+Insights%3A+What+do+we+know+about+our+eBook+readers%3F%22%3A&oq=kobo&aqs=chrome.0.69i59j46i67i199i433i465j0i20i263i433i512j0i67j0i131i433i512j0i67i131i433j69i60l2.1441j0j7&sourceid=chrome&ie=UTF-8).