SEO nowadays has far more to do with high quality, well-structured content than it does with backlinks.
Sorry, but no. Links which you place yourself are regarded as pretty much worthless by search engines, and if done to excess, will be seen as deliberate manipulation, resulting in your site being penalised.
Reputable blogs and sites will, in any case, mark user-submitted links nofollow (as we do here), rendering them useless for SEO.
I*n addition, while Google still uses PageRank in its algorithms, it has long since ceased to publish regular public updates, so any information you may find on PR is at best seriously outdated. Also, PR is calculated per page, not per site. It is possible for a site to have a high PR home page and very low PR internal pages, where your link may appear.