Several things can cause this problem:
- Make sure you have a copy of Adobe Reader installed on your computer. It is needed to display PDF documents.
- Try saving the document to your computer. First right click on the PDF link. A menu will appear, choose "Save Target As" or "Save Link As" from the menu. When the dialog box appears select a location to save the document and click on the save button. The file is now saved and you can open the document from your computer.
- Try changing your preferences in Adobe Acrobat. Open Adobe Acrobat from the start menu of your computer. Click on Edit in the top menu. From the list that appears choose preferences. A box will appear; click on "Internet" on the left side of the page. Remove the check mark in the box next to "Display PDF in browser". In older versions of Adobe this may be called "Web browser integration".