The monetization of downloadable files associated with a custodial host site based on resolving custodianship to a referrer publisher with subsequent presentation of monetized content within a modal overlay is disclosed. A request from a client device has a resource identifier and a referrer publisher identifier. The request for the downloadable file is evaluated against one or more publisher and custodianship policy rules, which relate to a file extension of the downloadable file, a format of the resource identifier, a custodial domain on which the downloadable file is stored, and a referral domain as specified in the referrer publisher identifier. When custodianship is resolved, a modal overlay on which monetized content is incorporated is presented on the client device. The modal overlay is concurrently displayed with the transfer of the downloadable file to the client device.