This is how you can add Google Adwords Conversion Tracker script in ExpressionEngine. First look up where your footer.php is placed in the filesystem. In my case it was ee_companyname/templates/_includes/footer.php
In the file you have to add a condition based on the URI. In ExpressionEngine you have a special kind of script and not regular PHP as you can see below. Segments of the path is stored in the variables like segement_[n]. In my case the condition was that the first part of the path should be tilaa-netin-kautta/kiitos to execute the conversion script.