Error message when downloading Digital Editions 4.5

[loish56919063]

I have downloaded Adobe Digital Editions, but get this error message...

"Digital Editions 4.5 Installer.pkg" can't be opened because it is from an unidentified developer.

Your security preferences allow installation of only apps from the Mac App Store and identified developers.

"Digital Editions 4.5 Installer.pkg" is on the disk image "ADE 4.5 Installer.dmg".  Safari downloaded this disk image today at 9:27 p.m. from www.adobe.com

I am lost.. trying to set up my Kobo so that I can get books from my library.  The instructions say to click Help at the top of the screen to Authorize Computer.  There is no "HELP"   I have admin rights... do I have to change preferences to allow other developers to install?

Help...

[joshuak12399059]

I had this same problem on my mac and the following worked for me.

Hold down the control button and then click the dmg and select open.

The installer window will popup.

Do the same thing to the installation package; hold down the control button, click it and select open.

[steelealexander]

I have the same problem.  Why is Adobe an unidentified developer?  Makes this software seem really ghetto...