Normally to ease the download process and remove the need for people to click on 8 different links we orgnaised the files in to a single compressed file for single secure download.
This is where the problem you experienced occurred. Unfortunately due to a security restriction on the Google Nexus, non-root users cannot open compressed files.
When this is the case, you would need to transfer the file to a computer then use the WinRAR software to extract it. After that, you have to copy the file back on Nexus 7, and then you can start to use it. This is annoying and wasting your time too. An alternative is to use an app like Astro file manager or Androzip file manager which can uncompress zip files.
Alternatively, we may need to set up a non-compressed download location for you to be able to access the files.
For further assistance please reach out to our support team here