If a computer has Adobe Reader and Adobe Acrobat then it is necessary to choose between the two programs for the default program to open a pdf file. Adobe Acrobat will open the AC pdf file in a separate window which is annoying. In Windows XP right-click on a pdf file that is not in AC and select Open With. Choose Adobe Reader and look for the button for the computer to always use this program to open the pdf file. In Windows 7 right-click on a pdf file and select properties. Look for Type of File and Opens With and you will see a button for Change. You can select Adobe Reader.
