Fix dmg is damaged and cannot be opened issue on Mac

This post helps Fix App is damaged and cannot be opened. You should move it to the Trash. while trying to run some downloaded applications from the web on Mac OS X.

Solution 1: Change the security setting in Gatekeeper.
Apple menu > System Preferences… > Security & Privacy > General tab (refer to the below image) under the header "Allow applications downloaded from:".

Solution 2:
Disclaimer: Gatekeeper is there to protect your Mac from the malware that's ever increasing on the Internet. You should only use this solution with Apps that you fully trust. If you are just randomly downloading software and using this solution to bypass Gatekeeper, you will end up with a compromised system. So, use at your own risk.
The following section contains advanced Mac tips.
Step1. You will need a program like TextWrangler (free; @ itunes.apple.com/us/app/textwrangler/id404010395?mt=12) to open .plist files or the Property List Editor available in XCode@ developer.apple.com/xcode/.
Step 2: set the following key values in info.plist:
<key>CFBundleSignature</key>
<string>?</string>
Refer to the below image.

Solution 3:
Open your terminal and write sudo spctl --master-disable and hit Enter, exactly provide the password of your computer.