Hello,
I'm searching for a way to include a contact form programmatically in each article that is inside a specific category.
These articles will be a kind of "job opportunities", then the user will read the article and fill the form if is interested ... the site admin then should receive the email with the contact form including also the article information.
I've seen many plugin that could do something like this, but the site manager that will create the articles will not be skilled enought to insert a plugin code, better way will be to avoid reinsert the plugin code everytime an article is created ...
Is there a way to call the plugin by insert it in the com_content/blog template as an override ?

You can achieve this in different ways, you can determine what suits your needs.

First method would be to create an RSForm!Pro Module and publish it only the page with the articles from that specific category.( this implies creating a new Category List menu item )
The downside of this method is that it will display the form on the list view of the articles;

Second method would be to insert the RSForm! Pro placeholder inside the article {rsform formid};

Third method is to create an XTD button that inserts the placeholder on click;

Regarding the script to grab the article information, you can find more information below:
http://www.rsjoomla.com/support/documentation/view-article/645-automatically-grab-article-author-email.html
http://www.rsjoomla.com/support/documentation/view-knowledgebase/34-custom-scripting.html