Cleaning up copy/pastes from web pages is generally a bit messy, due to ambiguity about the line breaks.
It may be helpful to know that if you paste first into Word, and have the "view all" setting turned on to show all the "funny stuff" you'll often see two kinds of line breaks. The common one used in documents is the paragraph break (shown in Word as the "Pilcrow" ¶) and the other is a line break shown as a "broken arrow."
You can use Word to quickly "clean up" mixed line breaks, using the "Edit|Find" - or better, the "Edit|Replace" (Quick-key Alt-E, E) function.
In Word, you can find the "broken arrow" line break by putting "^011" in the "Find What" box. (without the quotes). You can also use that "code" in the "Replace With" box to insert the line break. (The character has ASCII value 011.)
In Word the "paragraph" character is a "misbred bastard combination" that can't be easily "coded" as an ASCII/Unicode character, but you can use "^p" to find it or to use it as a replacement for another character in Word Find/Replace.
If you put ^011 in the "Find What" box and ^p in the "Replace With" box, "Replace All" will make everything "paragraphs." (You could of course swap the box entries to make everything line breaks.)
If you replace ^p^p with ^p you get rid of all the "double paragraph breaks" - provided you repeat the "Replace All" until no changes are made. (Word may sometimes refuse to replace the "end of document" paragraph break, so if you don't get to "no replacements" after a few repeats, use "Find Next" to make sure that isn't hanging up the cleaning. It's safest to delete the first ¶ of the end pair manually.)
Before "pasting" into a conversion program you should of course Save As plain text to get rid of "extraneous Wordness" features, and may want to open the saved .txt in Notepad or other "cleaner" editor for the paste.
Most ABC scripts are short enough to clean up manually, if you use an editor that shows you what's there; but when you get a whole web page full of mixed linebreaks automation (global replace) may be useful.