When doubleclicking PDF documents from internet explorer, nothing happens, they donot launch reader and open the selected document, instead I have to right click and do a "save as".

Hello, and Welcome to techhelpforum.

Have you tried (re)installing the latest Acrobat Reader?

http://www.adobe.com/products/acrobat/readstep2.html

Another alternative is Foxit Reader. Less bulk and overhead;

http://www.foxitsoftware.com/pdf/rd_intro.php

I've been using it for a while now and it works well.

Another thing to check is wether or not Adobe is set as the default program for PDF files. A lot of times if there is not default set it won't allow you to open it.