What do you mean by "
downloaded iso file is working"? How did you test it?
Checking the downloaded ISO file integrity is not a must but it's highly recommended. There are different methods for that but all involve
md5 or
sha1 value somehow as it tells the correct result for integrity (md5 or sha1) algorithm. This algorithm reads given ISO file and calculate (md5 or sha1) value for it. If both values (calculated one and the other given on the web page) are the same there is extremely high probability that ISO file has transferred fully and correctly and also that it wasn't tampered somehow.
For Windows there are many programs like
this one to do it. Many programs for burning have also ability to check md5 or sha1 if you'll use optical media.
For install from USB flash stick you can see
this page.