You can install Adobe Digital Editions 4.0 in Mac OS X by following the steps below:
Click Download tab. Downloads page for Adobe Digital Editions appears.
Click Download Digital Edition 4.0 Macintosh (18.7 MB)
ADE_4.0_Installer.dmg file downloads to your computer.
Double-click ADE_4.0_Installer.dmg file from your computer, to start the installation process.
Click Continue to begin the installation process.
Select the destination for the drive where you want to install Adobe Digital Editions. Digital Editions only installs on the drive where Mac OS is installed. Once you have selected the destination, click Continue.
Click Install to begin the installation process.
Mac OS X asks that you authorize the installation. Enter an administrator account name and password to authorize the installation.
Click Close after the installation is complete.
If you have difficulties with the installation process, see Can’t Install Adobe Digital Editions