I have a website with pagerank 3. Let's say the domain is domainA.com But now I want to change my domain into domainB.com. What I mean change is, setup domainB.com and then copy/import all the content in domainA.com and make it domainB.com content now. I am using WordPress and I know how to update the links, and etc. I think I can use wildcard redirect to still maintain domainA.com permalink and redirect each of the post to domainB.com. My concern now is the pagerank. How to maintain the page rank and all the backlink I have for domainA.com? Thank you very much for advise.
I am afraid that you may lose those backlinks as they are being associated with your older domain but not sure about the pagerank.
that is not a problem. You have to do 301 redirect and redirect the domain in webmaster tools. it will pass page rank as well as backlinks. I have a site similar to that.
As I said, and as Garcia said, do a 301 Redirect on your server end and on Google Webmaster there is facility to let Google know that you are changing domains. There is guaranteed way of doing anything. But this is the best way, and it is the way Google recommends. However, I would only change domain names if I felt it would help my business in other ways, like branding, keyword ranking and so on.
If google recommends that, you should do it accordingly. This would be better for your site as well as your traffic, pagerank also. However, I don't understand one thing that what is need of taking such risk, try avoiding it or you can opt for a sub-domain instead.