2) Open google chrome (don't use incognito mode) and navigate to the forum thread you want to copy. Start on page 1. Click the browser extensions icon, then click the Autopagerize extension.
You should then be able to view all pages in that thread as one long page. But you may have to scroll a looooong way to the end for the last page.
3) Press ctrl + a in order to "select all" on the whole page. Then press ctrl + c to copy
4) Open a word processor and right click > paste without formatting. This will paste it as text only.
The text document will probably be looooong and may take a while to finish pasting
Alternately, you could save it as a pdf instead. For this, disregard step 3 and 4. Instead, right click the page > select "print." On the print screen, you can choose to save it as a .pdf, then cancel the print job.