If the software is prompting for a license upon startup, you likely installed the full "Allegro PCB Designer" instead of specifically selecting "Allegro Free Physical Viewer" during the installation process. Re-run the installer and ensure you select only the Free Viewer component.
The Free Physical Viewer is strictly "Read-Only." You can view layers, measure distances, highlight nets, and print, but you cannot move components or change traces. To edit, you must purchase a full license from Cadence. allegro free physical viewer 17.4 download
Cadence does not host the standalone viewer on a public file server. You must create a free account on their support portal to access the software. If the software is prompting for a license
However, the tool has significant limitations: it cannot edit designs, save changes, or create new layouts. It also does not support simulation, routing, or auto-placement. For these functions, a full Allegro license is required. To edit, you must purchase a full license from Cadence
The 17.4 viewer is backward compatible. It can open databases created in older versions (like 16.6, 15.7, etc.).