I have installed and re-installed Adobe Reader 8.1.2 multiple times on my Windows Vista operating system computer. When I open PDF files, I receive a message/pop-up to Buy or Register Adobe Acrobat 8 Professional. I do not want to purchase Adobe Acrobat so I press "QUIT". After I press "QUIT" I lose my PDF and have a blank browser. What should I do? It is driving me nuts!!