Can duplicate content within a site hurt rankings??

[tathagata]

Its may be a basic question to you guys. So, don't make fun of me.

I have this issue. A site of mine has various duplicate pages. Well not likely exact duplicated buy most of the content is copied from one to another.

So, does it going to hurt my site's SEO and rankings? If yes then how can I make it stop. Assuming the fact that I cannot delete the same (duplicated) pages. Any suggestions?!!