Apple Keynote within DropBox

DropBox claims to support .key files within DropBox, that is, the files need not be downloaded from DropBox, but rather they can be viewed within DropBox. DropBox claims to support files up to 5 TB, and I pay DropBox for premium usage.

I have a 2 GB (lots of videos) 64-slide Keynote uploaded to DropBox. The Keynote is password-protected from the File menu in Keynote. When accessing the file in DropBox, DropBox opens a password dialogue, but when the password is entered, DropBox sends a message saying that .key files are supported, but that something "went wrong" and this file must be downloaded before it can be viewed.

I contacted DropBox's support, and they acknowledge that DropBox supports .key files, but they could not tell me why I could not view the file within DropBox - they suggested I ask Apple.

Can I send a 2 GB password-protected Keynote to someone and have them open and view the presentation without downloading the presentation? Or must the presentation be downloaded first? Why? We tried uploading a non-password-protected version, but still got the DropBox error message requiring download.