I have not tried this, but seem like it is doable:
1) Zoom in on your word doc to the place where you need to sign.
2) Take out s-pen, push button, and hold on screen for 2 sec to take screenshot
3) Now you are in the Edit mode, sign it.
4) Don't save it, just use your s-pen, hold the button, and crop out your signature and it will auto save to clipboard.
5) Close the edited picture without saving it
6) Now you are back to your word doc, just insert the image from the clipboard to overlap where your signature is supposed to be.