You can append and merge individual sheets/models within the same multi-sheet file. Any duplicate geometry or markup is removed when sheets or models are merged.
For multi-sheet files, you can bring geometry and data from internal project sources, that is 2D sheets or 3D models listed in the Project Browser, into the currently open sheet or model. However, 3D models can only be merged/appended with other 3D models, and 2D models can only be merged/appended with other 2D sheets.
You can merge and append several sheets/models at once. However, you must select at least one/sheet model that matches the type of the currently open sheet/model.