process queryString and call function in a module

Hi,
I face the following problem:

I have several buttons on a node, which -when clicked- allows users to see a certain part of a documentation located on another node.
The links have the following structure:

http://www.example.com/Features.html?section=doc1
http://www.example.com/Features.html?section=doc2
etc.

When a button is clicked and the second node is shown the module should get the queryString section=docX and show the appropriate section of the documentation. For technical reasons I cannot use an anchor or the like. i have to open the documentation by code.

Now my question is, where should I place the code within the module to get the querystring and call the function to load the correct section of the documentation. Of course the function hast to be called before the second page is loaded.

Should I use the menu_hook for this? Is there another hook that should be used for that?
I read the documentation about modules, but it is still unclear to me, where to place the code.

Thanks in advance for your help
Dirk