You don't describe if you are trying to do this programmatically or manually, as part of a larger project or just a onetime effort for a document. That information is important for a specifically targeted answer. You do use the word "object" and "as" so I will assume, you want a VBA solution.
The only successful way to do this with Mac PowerPoint and Mac Word is to first export the PPT slides as images. Make sure you set the image quality (larger image sizes mean better quality) via the File > Export
dialog, when you choose the image file type to use.
The resultant image files from the Export will have names like Slide 1, Slide 2, Slide 3, etc. and you can then use the Selection.InlineShapes.addPicture(Filename)
to bring the slide images into your Word document.
Just in case you are not looking to write a programmatic solution yourself, there is a free add-in to Word (Windows and Mac versions) that will insert PowerPoint slide images into Word documents. Do a web search on AuthorTec Insert and you will find it.