I am running with Boundless Opengeo Suite on Linux based server to create a WebGIS application in forestry management. Everything is working fine (at least to this step that I am being stuck here).

In GeoExplorer, the default popup window for Editing (modify or create) is working well, but I want to customize it to attach another PostgreSQL referenced table within this popup windows, to attach files to the feature (something like the functionality in ArcGIS) using PHP (or Javascript). I have googled for several weeks, but still no luck.

Can anyone show me which file(s) (in GeoExplorer and/or in Geoserver) to be customized, or let me know if other open source alternatives are available on the earth?