If I copy free articles to my adsense website, is this allow? and How effective is this gonna drive traffic to my site? I know it's free content, so other people might use them as well. Should this makes the site difficult to rank high?
If that is all you do you will not do well with Google. You need your own content. After being indexed you can then add some FREE article content and Google will be happy. Also you need links from sites that come from the same genre. I would make sure you have at least 50% orginal content.
Yes it does. None of my free content pages ranked, stuff I got from Ezine Articles and other places like that. That place in particular has such a high PageRank it "knocks out" any competition. Nice little gig the webmaster there has going; you have to link to him if you use the articles and though he has like 60,000 you can only use a handful... keeps him up and everyone else down.
On the other hand, you can do the same if you write your own content and syndicate it out... or take advantage of someone w/ a higher pagerank sending traffic to your site.