[pluggo] runtime files trouble

I was hoping somebody might be able to clue me in as to why when I attempt to download any Pluggos that are out there, I only end up downloading a seemingly useless document (the kind I can't open). 

I'm using OSX on an Intel Macbook and I believe I installed the Pluggo Runtime properly (in order to be able to download free Pluggos only, for now)

I'm new to a lot of this and definitely have some blind spots. Does anyone know what I'm talking about or what I might be missing here?

Much Thanks, J