how to use pdf reader module in drupal?
You need to enable pdf module and create a file field in the content type where you want pdf to be visible and there are two option to display PDF file in the field display setting, select which ever you require. (You need to use the latest pdf.js to use first page display).

Note: you need to download pdf.js manually and add in project directory

Hope you are following this,
http://drupalcode.org/project/pdf.git/blob_plain/refs/heads/7.x-1.x:/README.txt