Refilling paragraphs to remove hard returns?

[jester@panix.com (Jesse Sheidlower)]

I imagine this is a common problem, so I don't know why I'm
having so much trouble finding an answer.

Suppose I have a text document that I've worked on in
text-mode. It is filled using the usual fill tools, so it
wraps at 72 characters, with a hard return after each line.
Paragraphs are separated by an extra hard return; there's no
other indentation.

I now need to give this document to someone who wants to work
on it in a word processor, who complains that there are hard
returns after every line. What's the easy way to remove these?

Going forward, I could work on such documents in
longlines-mode. But it's not clear how to fix what I have. The
trick mentioned in the Emacs wiki of resetting fill-column to
a large number and then refilling the region doesn't work,
because each paragraph is seen as one line, rather than the
block of text set off by two newlines. Yes, I can regex
replace all examples of return (not followed by another
return) with a space, but I'd think there must be something
more organic.

What trick am I missing?

Thanks.

Jesse Sheidlower