"Copy drawing to project" functionality in Plant 3D needs to have the ability to access directly from Vault, only possible from local store.
Currently you are required to create all files in Plant 3D first, then share them with the rest of the design team, or
Have the file outside the project drawing store in Vault (not in the project 3D Model DWG path), then you are able to copy to project, but results in duplicate files in Vault.