After installing 7-Zip, you can simply double-click a DMG file to open it and browse its contents. I'll go to my downloads folder in the doc and it won't do anything.
All that happens is that I click on the DMG file, and then it doesn't respond. Now I'm trying to install the VPN with the DMG file but it doesn't open. I opened a DMG file when I needed to install chrome and there were no issues with that.
Download again and wait for the download to complete before opening the DMG file. After downloading the Mac OSX SimUText installer file, the DMG fails to mount, or you see a second DMG file including the word, 'Part' Action: The installer DMG file did not fully download, the download was interrupted, or otherwise damaged.