I'm not aware of any way to take a Word document and paste it in that keeps formatting or images specific to that document without doing something like saving it as a PDF--which is basically a picture of how you think it should look--and uploading that image.
I use formatting and images in my newsletter, but I upload the images separately and do the formatting using the editor provided so the document has the correct HTML coding to appear properly for both text and graphical email clients.
It was a bit of a struggle to set up the first one but I just clone it now and replace the text and images from the last one with the new text, but my business model is "boring and lazy" so I'm on brand.
😁