Not sure about the question ... legality or process? Legality, I bow out ... the process ... well, here we go:
Display that story on your computer via the format in which it was entered or some other that works ... MS Word, Adobe PDF, what ever.
Put your cursor at the top left of the text, left click and hold that button down, and move the cursor to the end of the document. Not sure how this works on everyone's computer, but, on mine, that text selection is now highlighted in blue.
Now, you need to 'copy' that text ... I'd just do Ctrl-c (hold down the control key and press 'c') or, you could right click on that area you just selected ... a window will pop up ... click on the 'Copy' line.
Now, go to the WikiTree profile and put your cursor where you want that text to be. Yep, my answer would be Ctrl-v ... or you could right click again and select 'Paste'.
You're done ... well, unless the question was about legality ...