Did you install warframe before it was on steam? Do you just dislike steam and never bothered installing it, but you want the new tennogen stuff (or just the artifically inflated steam play-time to brag about)?
How to share your warframe install between the steam and nonsteam versions of the game without reinstalling:
If you previously installed steam warframe, but deleted the folder: go to steam > library > warframe > delete local files. this wont remove any of the appdata non-steam install.
Begin steam warframe fresh download.
Wait about a minute.
Stop and cancel the download from steam download manager.
Close steam completely.
Go to C:\Steam\SteamApps\downloading and delete folder 230410 and the matching 230410_(something).patch file (these are pre-allocated space and use 17GB on your drive wben before download)
Go to C:\Steam\SteamApps and open appmanifest_230410.acf in notepad, find StateFlags = 1026, chance 1026 to 4. save and close. This tells steam that warframe finished downloading.
Locate your warframe public build install (the non-steam game), it should be under C:\Users\USERNAME\AppData\Local\Warframe\Downloaded\Public. !! Check the folder size to make sure it is over 16GB. If it is not, you may have installed warframe in programfiles or system root. !! The launcher insists on putting itself in appdata/local no matter where the game is installed.
You will need the LinkShellExtension program to do this (Unless you are a cool geek and know how to make a junction from the commandline). it is a very small addon that gives you a symbolic link menu in the file rightclick menu
Symbolic links let you "shortcut" a folder to another location, allowing programs to access the folder like it is in two places at once, saving tons of disk space. You can even use this to run the same program easily on multiple OSes and drives, for a computer running two versions of windows, but that is another story.
The download and explanation. http://www.howtogeek.com/howto/16226/complete-guide-to-symbolic-links-symlinks-on-windows-or-linux/
Rightclick the folder Public and choose "pick link source"
Go to C:\Steam\SteamApps\common, rightclick and choose "Drop As" > "Junction" and rename the junction "Public" to to "Warframe". A junction seems to work better than other types of links for this.
Registry files: If you never ran steam warframe before, it may help to copy the following into a text file, save it as .reg instead of .txt, and run it. This will put these settings into your registry.
________ Copy everything below this line ________
Windows Registry Editor Version 5.00
Run steam, select Warframe > properties > local files > verify install
Run warframe from steam.
Look at cool tennogen stuff.
Run normal warframe from your old shortcut, if you feel like it. It still works fine too!
You can now run either one at any time, no downloads required.