Yup you can upload all sorts of files but preferred text format is pdf for this which you can select as a "save as"/"download as"/"export as" option in most text formatting software.
epub is also encouraged for Ereaders but that is more tricky to pull off and not required.
but if you are interested the easiest way I know of to do it is to load the word/wordx file into Caliber ( https://calibre-ebook.com/) and converting it to epub before checking it. Caliber also is great for converting word/wordX to pdf and also allows you to set a full page a4 cover art page without margins if you have one made up in jpeg/png/tiff.