Hello, My site Pr is 4 and now I want to design it in wordpress or joomla. I will use same old content available on site( or may be change little bit content and pages) So does it will effect my Pr ? Because I don't want to loose my Pr...all suggestions will help me alot...ASAP!!!
NO, your PR will be the same the quality and the quantity of backlinks is very important and as Cernus says you should have same content and add content more often and you will get HQ links to your website easy and fast...maybe not that fast but those links will matter for PR. Good Luck!
Redesigning the site won't hurt your PR as long as it is just the design you are changing not the content or the format of the current links.
While I agree with some things that have been said here, I also disagree on some points. A site conversion to Wordpress and or Joomla could certainly impact your PR, rankings and pages indexed. If you keep the content the same and the site structure the same, you will most likely be OK. However, think about this: if you convert to WP, your URL's could potentially change. If they change, any links that you have pointing to those old Url's now have little value. Without those links, your site positioning will certainly change. As long as you keep everything as close to the same between old and new, you should be OK. By everything, I mean same URL, image names, page names, titles, descriptions, etc. Any variances could potentially impact you. I learned the hard way with my first major conversion from HTML to WP. Good luck.
Whether your PR changes has nothing to do with the content of the pages remaining the same. You can change every word on the page and your PR should remain the same. PR is simply a measure of a URL's link popularity... a measure of the quantity and strength of inbound links to the URL. Whether or not your PR changes as a result of a redesign or going to a different blog platform has to do with your pages' inbound links - both inbound links from external sites as well as internal pages. If your URLs change and you fail to 301 redirect all old URLs with inbound links from external sites to new URLs then the only source of PR will now be links from internal pages which means you will most likely see a drop in PR. You should 301 redirect each old URL to the new URL whose content most closely resembles the content of the page at the old URL. This way not only will the new URL get credit for all of the old URL's inbound links (i.e. get credit for the PR) from external pages, but the link text used in those links will have the best chance of helping your rankings since they should be relevant to the new URL's content as well. If you change the way pages on your site interlink (navigation, footers, breadcrumbs, etc.) then you could see PR changes as well. Changing the way pages on your site interlink can influence your PR positively or negatively depending on whether the new linking structure is better or worse than the previous linking structure, respectively.
Let me just add to my brief statement. Don't worry about PR, worry about your rankings. The only thing I find PR good for is being able to charge more for advertising.