A page image is a snapshot of the layout
An INDD layout stores page elements and editing information, while PNG stores a fixed grid of pixels. The exported image can be placed in a slide or preview, but it does not retain editable text frames, vector paths, or the layout's linked assets.
Keep the source project as the authoritative version. If a headline or photo changes, update the INDD document and create a new PNG instead of repeatedly editing or enlarging a raster copy.