See http://www.word.mvps.org/FAQs/Formatting/CleanWebText.htm

If that site doesn't answer it for you, you might try wildcards and variables.
What I've done in the past is find some of the rogue paragraphs by either
inserting a random character combination around the paragraph semi-manually
then replacing that text with what I want automatically.  or if you know that
the carriage returns are always surrounded by a certain set of characters you
can do the wild card searches.  For example:

[A-Za-Z0-9]^13[A-Za-z0-9]  This finds returns marks between any letter or
number
_^13_   finds a carriage return between spaces (replace _ with the spacebar)
or you could combine the two as below:
[A-Za-Z0-9] ^13 [A-Za-z0-9]  (space on either side of the ^13)

You can also add other characters or symbols to help or utilize a not
function.
If the carriage return appears always after one word in a line something
like this might be what you are looking for (substitute _ for space bar):
_[A-Za-Z]*[a-z]^13

I might even use a replace with grouping as:
In the find box:  (_[A-Za-Z]*[a-z])(^13)
In the Replace box:  \1

This probably won't find words that are two letters(ie. at, a, an, etc.),
but you could probably remove those few by hand or use a different search to
help you.

ps. make sure wildcards is checked under options