There's another option I would use, which I consider slightly easier and
more straightforward than the methods described on this particular website
(I've only had a quick look at it):
Copy the text in your first document. In your second document, place the
cursor where you want the text to appear, then click Edit>Paste Special. On
the left side of the window that pops up, you'll see two options, Paste and
Paste Link. Select Paste Link, then determine the format in which you'd like
the paragraph to be pasted. Hit OK, and you'll see the text appear in your
second document, as if you'd simply pasted it. Save the file, close it, and
if you now make changes to the paragraph in the first document and save it,
you should get a message when you open the second document, asking you if
you want to update the document so it reflects the changes made in the first
document. If this method is not sophisticated enough, you'd better follow
the instructions which Bob posted.