Invalid Download (also first-timer)

[cherbxmm]

After watching the how-to download video. I cannot figure out why I cannot open the downloaded file on my computer.
I am specifically trying to download Calculus 2 with Master Sorcerer. Whenever I try to open the encrypted file it says: Window Cannot open the file. No error description.

Am I doing something wrong in the process?

Thank you in advance for any help/advice.