MacBook Pro: Cannt run install .. 'no application set to open document'

hi.
*** i’m trying to download a second copy of cubase to my old MacBook pro 2010 **

i’m trying to install a copy of cubase (AI LE) 9.5 full ( i bought the 9.5 update from LE i think)
I downloaded it via the STEINBERG DOWNLOAD ASSISTANT…
I looked at the downloaded files…
when i click on the filename listed just below… i get this message

There is no application set to open the document :
Cubase Le AI Elements 9.5 installer mac dmg sda-download

The icon next to the filename looks like a ‘document’ and the type shows as DOCUMENT. not as an application …etc

what is going on ?
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if i do install a second copy onto my laptop… can i use the same activation code i used to download on my desktop ?
or must i ‘reactivate’ the software on my laptop ? There is information all over the place on this … kind of bewildering
I know all this is to prevent piracy… but its confusing to me… i believe the licence allows me to load cubase on more than one pC
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thanks
steve

Duplicate post