I have a site where all content is inside main.php?page=nameofpage. If page=about, than about company information shows. Now I will delete contact from main.php and create own static page company_name.php for it and buy some links for it. I am worried what will happen when google index company_name.php, but still don't delete history of main.php?page=contact. Will this count as duplicate and won't be so good success? Should I write for any case another text?
I am currently involved in doing the same thing. You will need to create 301 redirects. This tells Google that a specific page has permanently moved. Google it for more info. Here is one site with some explanations: http://www.webconfs.com/how-to-redirect-a-webpage.php