1. A digital computing device for viewing shared annotations of at least one electronic reference document, the device comprising a digital memory, a display, a user input interface, and a network interface; and said computing device being configured to: receive, over a network, via the network interface, a digital location identifier for navigation to a shared reading location with an associated annotation, said digital location identifier specifying the shared reading location within a version of the electronic reference document and does not include the version of the electronic reference document; upon receipt of a selection to navigate to the shared reading location, determine if a user of the digital computing device has sufficient rights to use a copy of the electronic reference document referenced by the digital location identifier, and, if the user does not have sufficient rights, (i) provide a prompt with an option for the user to purchase said rights, (ii) responsive to confirmation of the purchase of the rights to use the copy of the electronic reference document, receive the copy of the electronic reference document, and (iii) store the copy of the electronic reference document in the digital memory; and upon successful confirmation of the user's rights to use the copy of the electronic reference document and responsive to the selection to navigate to the shared reading location (i) determining that the content referenced by the digital location identifier exists in the copy of the reference document, (ii) displaying at least a portion of the copy of the electronic reference document at the shared reading location and the associated annotation within the copy of the electronic reference document at the shared reading location.
1. A digital computing device for viewing shared annotations of at least one electronic reference document, the device comprising a digital memory, a display, a user input interface, and a network interface; and said computing device being configured to: receive, over a network, via the network interface, a digital location identifier for navigation to a shared reading location with an associated annotation, said digital location identifier specifying the shared reading location within a version of the electronic reference document and does not include the version of the electronic reference document; upon receipt of a selection to navigate to the shared reading location, determine if a user of the digital computing device has sufficient rights to use a copy of the electronic reference document referenced by the digital location identifier, and, if the user does not have sufficient rights, (i) provide a prompt with an option for the user to purchase said rights, (ii) responsive to confirmation of the purchase of the rights to use the copy of the electronic reference document, receive the copy of the electronic reference document, and (iii) store the copy of the electronic reference document in the digital memory; and upon successful confirmation of the user's rights to use the copy of the electronic reference document and responsive to the selection to navigate to the shared reading location (i) determining that the content referenced by the digital location identifier exists in the copy of the reference document, (ii) displaying at least a portion of the copy of the electronic reference document at the shared reading location and the associated annotation within the copy of the electronic reference document at the shared reading location. 6. The computing device of claim 1 , wherein upon successful confirmation of the user's rights to use the copy of the electronic reference document, the display of the electronic computing device displays a plurality of annotations received from one or more other electronic devices, each associated with a corresponding reading location within the reference document.