What is your OS?
What is your Reader version ?You can get the version from here: Launch Reader from your /Applications folder > From Menu choose Adobe Reader >About Reader
What is your Safari Version?
Do you have any other Adobe Reader or Acrobat installed on your system?
Please try this:
1. Quit Safari
2. Launch Adobe Reader from /Application folder : At this point you should be prompted with End Users Dialog.Accept the end users
3. Open PDF in Safari.
