9. The computer program product of claim 6 wherein a first one of the plurality of links is associated with a first version of the second electronic document, a second one of the plurality of links is associated with a second version of the second electronic document, and the processor is operative to select at least one of the plurality of links by selecting one of the first one of the plurality of links and the second one of the plurality of links based at least in part on user preferences relating to first and second document portals associated with the respective first and second ones of the plurality of links.
6. A computer program product comprising a non-transitory computer-readable storage medium having program code embodied therein, wherein execution of the program code by a processor causes the processor: to detect a reference citation in a 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; to select at least one of the plurality of links based on preference information; and to control display of the selected at least one link and at least a portion of the first electronic document; wherein the program code when executed causes the processor 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.