An electronic device with a display and a touch-sensitive surface displays a portion of a document in a primary user interface for the document. The portion of the document includes a respective author-specified term. The respective author-specified term is associated with corresponding additional information supplied by an author of the document, and the corresponding additional information is not concurrently displayed with the author-specified term in the portion of the document. The device also receives a request to annotate the respective author-specified term in the portion of the document; and in response to the request to annotate the respective author-specified term: annotates the respective author-specified term in the primary user interface; and generates instructions for displaying, in a supplemental user interface for the document distinct from the primary user interface, the respective author-specified term and at least a portion of the corresponding additional information for the respective author-specified term.