Check the MD5
The first thing you need to do with most of these downloads is check the MD5. The MD5 is a checksum that is calculated on the file size and is used to make sure you do not have a corrupt download. It is very simple to check the MD5 of a file, some Android File Managers have an MD5 calculator built in, but you can always download an MD5 Calculator to your computer and check the file that way.
MD5 Calculator for PC: WinMD5Sum
MD5 Calculator for Mac: MD5 for Mac
Both of these are free downloads – Please make good use of them!