Exactly how does Google deal with Duplicate content

Duplicate Content

[total amateur]

Hi,

Seeking advice from the Guru's on here.

I have a small web site which is doing very well on Google. (Mainly due to the information obtained on here.)

Shortly I shall be adding a fair amount of new content. This will be taken from a Government site (With their permission)

Was thinking of using robots.txt to ban all spiders from the new files and placing "nofollow" in all my internal links.

However, there is a strong possibility that other sites will link to these pages, so the search engines will eventually find them.

So, if I am hit with a "Duplicate content" penalty what exactly will be the result.

Will just the duplicate pages not show up in the SERPS or will my entire site suffer ?

Thanks

[superpower]

The new content may be tagged as "supplemental" which means it will in most cases appear below results in the main index, OR if you are lucky it will not be supplemental or counted as dupe content.

Generally you will not be completely knocked out of the main index for all your pages or have your whole domain degraded unless you are doing blackhat stuff.

At least this is my experience, and I have both scenarios on 2 different sites.