Is there any way to add adsense after few paragraphs in blogs and forum ?

Sorry, I don't know of any way to put it after a few paragraphs as that would have to take the string stored in the database and break it down to put the google code between paragraphs before it is present on the screen.

I do know where you can display text/variable after the blog and before the posted in categories text.

Phpfox discourages changing the code and will not be responsible, so do at your own risk.  Always remember to have a backup copy in case you mess up your site..and believe me we all do that at least once (myself a dozen times)

For blogs go to file

PF.Site/Apps/core-blogs/views/controller/view.html.php

after line 39 where it says {$aItem.text|parse}

if you paste the variable below, this blogs current category should show up right after the blog.

{$sCategories}

The issue is going to be whether or not Google AdSense code works in a template as everything has to be enclosed in curly brackets unless it is CSS.  Not sure if you can slap some code in there and it will work.

If that works then I will look up the forum spot for you :)