The CAD tool developers typically offer “Free Viewers of Browsers” to enable viewing and often marking up the design.  They may also offer viewers with even more capabilities for a nominal cost. 

Cadence’s Allegro Physical Viewer
Database viewer for Allegro PCB Editor, Allegro PCB SI, and Allegro IC package solutions.  Allegro Physical Viewer includes all of the features of Allegro FREE Physical Viewer plus property and element query, measure distance, find, reports, and more.

 Mentors’ Expedition Free Viewer

 Valor’s Universal Viewer