1. An apparatus comprising: a processor; a memory coupled to the processor; and a display; wherein the memory stores a first electronic document; and wherein the processor is operative: to detect a reference citation in the first electronic document; to process the reference citation to determine a plurality of links to a second electronic document identified by the reference citation, each of the plurality of links comprising a uniform resource identifier (URI) for directly accessing the second electronic document; and to select at least one of the plurality of links based on preference information, and to control presentation of the selected at least one link and at least a portion of the first electronic document on the display; and wherein the processor is operative to process the reference citation to determine the plurality of links by: formulating a search query based on the reference citation; identifying a plurality of document portals, the plurality of document portals comprising a first subset of document portals for which a particular user is known to have a valid subscription and a second subset of document portals for which a particular user is not known to have a valid subscription; restricting the search query to the first subset of the plurality of document portals; executing the restricted search query; and in the event that executing the restricted search query fails, executing an unrestricted search query to search the second subset of the plurality of document portals.