Hi, I have written some articles on a forum, but now I want those articles on a new webpage. I can go to the forum and delete all of the articles, but my question is how will this effect the duplicate content thing that Google has? Will it still consider it duplicate content if the original is deleted?
Do not worry about the search engines, just concentrate on your user experience. ... To answer your question if the forum content was already indexed and you copy it to a new web page it will be considered duplicate content.
This is tricky as many marketers believe that Google is very aggressive with its duplicate content filter. Even if you were to 301 redirect it, which should be the solution, there is a possibility that for some time Google may loose track of the content as 301 redirects can take weeks or even months to be fully transfered. If the articles are syndicated then it may be another issue. This is an area that there are few definitives and based on experience, when it comes to syndicated content there's a lot of guess work and trial and error. If the articles are not syndicated, then you technically should be able to just 301 redirect the articles to the new location and be fine.
i agree with seoimage, do the redirect to the new page. You may lose some rankings for a short period, but rankings should return to normal over time.