1. A computer system, comprising: a processor; and a memory comprising program instructions executable by the processor to: topically segment digital documents into topical segments; extract key concepts from the topical segments; extract key phrases from the topical segments; select a first one of the key phrases that is included in a first one of the digital documents; compare the first key phrase with the key concepts for similarities; rank the compared key concepts by the similarities; identify, from the topical segments, those topical segments in the first digital document and a second one of the digital documents that have ranked key concepts with individual similarities above a specified similarity threshold; establish navigation links between the first key phrase in the first digital document and the identified topical segments in the first digital document and the second digital document to enable a user to navigate within the first digital document or from the first digital document to the second digital document; and concurrently display at least: a currently viewed topical segment in the first digital document, first individual navigation links to a previous identified topical segment in the first digital document and a subsequent identified topical segment in the first digital document, and a second individual navigation link to an identified topical segment in the second digital document.