Rise of Tomb Raider using download from here then buying.

I download Rise of the Tomb Raider from here. The crack still isn’t out so I decided to just buy the game but my question is do I have to re-download from Steam or can I just open the version from here, which launches Steam to run the game. In essence will Steam flag the game in any way because I downloaded it from a different source than them.
Answer #1
I used this method to get Batman Arkham Knight into steam, it will work with Tomb Raider. Install the game and then copy the main folder into the directory C:\Program Files (x86)\Steam\steamapps. Then open steam and then the next time you open Steam, it will find the game and “rebuild it”. (This did fail the first time I tried and had to copy and paste the rebuilt info back into the above link, probably wont happen, but can be a little bit of a pain, but can be done..)
Also heres a link for 35$US of Tomb Raider if needed..
http://www.cdkeyhouse.com/
Answer #2
Usually not a big deal, I’ve done if not all of my games via this method. Saved a ~ censored ~ of bandwidth.