Convert... performs a batch export of RealCADD files to DWG – but only if you originally had the Professional version and have been moving the "RCADtoDWG" file in to the same folder that contains your RealCADD application.
To convert your files, it's best to put them all in a dedicated folder. When you click "Convert..." it will open a Finder window. Navigate in the usual way to where your folder is located and click the "Open" button at the bottom right. RealCADD will export all the RealCADD files in the folder to DWG format. It will leave the original RealCADD files in the folder.