This extension will allow you to upload pdf in your system. Not only that but also it will allow you set those uploaded pdf for specific products. Then finally it will be visible under the product description of that select product in front end. It is MULTY LANGUAGE SUPPORTED and MULTY STORE SUPPORTED. Fully SEO FRIENDLY and object oriented. So, you will never fetch any code conflict. All of my codes and database tables are totally separate. So, your default codes and functionality should not interrupt. Everything done based on OCMOD