The process of adding the new pages on the website will decrease the PR value of the site. The reason is that the existing pages will lose their pagerank value to the new pages added. Most of the big website that contain lots of pages and information will lose the significant PR compared to small sites.

The backlinks from the related sites as well as quality site will add significant pagerank. It helps when the website is valued for pagerank. Link from quality and good site illustrates Google that your site is significant and it should be given higher pagerank value.

When the site you have linked is banned by Google, then even your site has the possibility of banning. So, when you link to a site check always it is a proper site.

The Google analyze the content of the website and shows the relevant website as per your query and the pagerank is not important as you think.