how can I add the objects we have produced on the viewer by drag and drop. Like adding a window to the wall of the house? Is there an example or application made for this? or a resource you can recommend?
As shown in https://forge.autodesk.com/blog/dynamic-model-placement you can load and move models around using their placementTransform: model.getPlacementTransform() / model.setPlacementTransform()
You can also combine this with the drag and drop functionality of the browser. Once the user reached the Viewer while dragging, we can start loading the given model. Once the model is loaded, as the user keeps dragging around we can modify the placement of the dragged model. See https://forge.autodesk.com/blog/drag-and-drop-models-viewer