So Portal is currently on sale at the almighty Steam for $USD1.99. 
 
And I got the complimentary version that day is was free. 
 
I was wondering, if I bought this other portal, would I get two sets of achievements? Cause the free one isn't just called straight up 'portal' in my account info, it's named 'Portal - Complimentary (Opt In)'. 
 
So yeah, two sets? (I am assuming the free one has acheivements ... I should actually play it one day :D )

No, you will not get double achievements for something like that. The bigger question is, why would you pay 2 bucks for a game you already own, just for the achievements?

" No, you will not get double achievements for something like that. The bigger question is, why would you pay 2 bucks for a game you already own, just for the achievements? "

Yes, the free one has achievements. I doubt you would get more by getting a second copy though.

It wouldn't even let you purchase it again if you already have it in your library. Don't feel bad about taking it when it was free, they wanted to give it to as many people as possible. They keep putting it on sale to advertise it, and get as many people to buy it as they can, so more people will buy Portal 2. They're more focused on making profit from that than Portal now.
 
But if you really wanna pay for it, you could buy it as a gift for a friend.