Some lead-gen companies have a database of subscribers who they’ve segmented. They send eblasts under the names of their “publications” which are emails containing download links for their clients’ white papers. Recipients who download are sent to clients as leads. Since they already have these individuals in their databases, they don’t need lead forms for users that click from email. Make a report of everyone who clicked download and send it to the client.
Other companies are agencies and platforms that buy from data owners. Some of these companies are listed on my marketing resources page.