There may well be more technically satisfying ways to do it but I'd have thought the easiest is to take good photo of the document, save it and then you can load as any normal image for e-bay.
It’s possible you may only be allowed to sell the printed product anyway, rather than the Word doc as a file.
I had a large batch of my own general knowledge crosswords and wanted to sell to anyone who might be able to use them in a magazine. Ebay removed the ad because I was offering a product in file format which, it turned out, was an infringement.
So best course may be to print it at high quality and photograph it.
Perhaps if one indicated the text and said it can be supplied in the following formats ..... then eBay may not have such an issue ? After all you are selling the work you put in, the format is subsidiary.
Beware of photoing too much though. Someone may copy the picture and OCR it for free.