Restrict your Google results to the filetype and/or country of your preference.
This is NOT a standard feature of the Google search engine.
Check out as follows:
Fill in your combination of words to search for. Then decide on filetype and country.
Finish with clicking the Advanced Googling button.
Google customized searching
The example underneath works on the principle of a site-flavored Google.
This means that Google optimizes its search results for a given profile.
Here the profile chosen was Computers with the following subjects:
Hardware - Internet - Operating Systems - Programming - Software
This second example is customized on Science and Astronomy only.