There is an established site (domain and content) which need promotion. Instead of building backlinks and doing other SEO work, there is an option to get another domain (wiht some content) which already has high rankings and PR. Are there any risks of being punished by search engines (like Google) by downgrading the raitings, if I take the whole content of one site (low PR and not many backlinks) and put it to another domain with a better rankings and more backlinks? The other domain has been used for the same niche, so content will be relevant to its previous content. Thank you
You could take the content from the older site and put it on the new site and leave 301 redirects to the new content. This tells Google that the content has been permanently moved to the new website, therefore you will get no penalties.