Open PDF documents in SharePoint
SharePoint is capable of opening PDF documents however there has been a change since SharePoint 2007 which could open PDFs be default. The enhanced security features of SharePoint 2010 mandates that you must manually adjust the security settings to view PDFs otherwise users will only be able to download the PDF and not view it.
In General Settings for the SharePoint site set the Browser File Handling to Permissive. You then need to restart IIS for the changes to have effect.
Note that the Browser File Handling setting is specific to each site and so this procedure must be repeated for all sub-sites which need to display PDFs.