After you install Acrobat or Reader on Windows 7 or Vista, icons of all applications and file types change to Acrobat/Reader icon. Double-clicking any icon or file launches Acrobat or Reader. (The native application associated to the file type doesn't open.)
Disclaimer: The registry contains system-related information that is critical to your computer and applications. Before modifying the registry, be sure to make a backup copy of it (Windows 7, Windows Vista). Adobe doesn't provide support for problems that can arise from improperly modifying the registry. Adobe strongly recommends that you have experience editing system files before you modify the registry. For information on the Windows Registry Editor, see the documentation for Windows or contact Microsoft Technical Support.
For more information, see Log in using built in-administrator | Create local administrator account | Windows 7, 8, Vista.