This bit here:

Code:
$uninst=ReadValue("HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Adobe Acrobat 7.0","UninstallString")
If $uninst<>""
If Exist ("C:\Program Files\Adobe\Acrobat 7.0\Acrobat\Acrobat.exe") Exit EndIf

...is missing an "endif"

If I'm reading that right, also, you're exiting the gosub if Acrobat.exe exists before it ever gets uninstalled.

Code:
$uninst=ReadValue("HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Adobe Acrobat 7.0","UninstallString")
If $uninst <> ""
     If Exist("C:\Program Files\Adobe\Acrobat 7.0\Acrobat\Acrobat.exe")
          <here is where you'd perform the uninstall>
     EndIf
EndIf

...seems more like the ticket.