I had to dig five links deep before I got an answer. DocSend is a service that allows founding teams to send pitch decks to investors. DocSend invited founding teams to participate in this research.[0] It's worth noting that they don't seem like they asked for consent from the VCs whose browsing behavior they observed for this study.
In DocSend's privacy policy[1], the VCs are Viewers, whereas the founding team is the User. DocSend apparently allows Users to give consent on behalf of the Viewers:
>If you are a Viewer who views Content you receive from a User via the Service, we automatically collect information about your interaction with such Content and our Service. The information we collect includes: Whether or not a you have viewed or are viewing Content; Date and time you viewed the Content; Number of times and length of time Content was viewed; Which portions of the Content were viewed; and Your IP address and location.