How to use DLLs

Hello Guys

Im trying to use a C# DLLS called System.Data. So first I ve created a folder in Assets called Plugins and then i pasted the System.Data there and opened Mono Develpment. After this I right clicked in references > Edit References > .net Assemblies and there was my DLL there. So i marked the DLL and pressed OK and then in code i used using System.Data. Have done all my code there with no errors been pointed by Mono Development. Saved my code and got back to Unity Inspector and it said:
erro CS0234: The type or namespace name ‘Data’ does not exist in the namespace ‘System’, are you missing ‘System.data’ assembly reference?

I`ve made a lot of research to find answers and got nothing to solve this.

My unity version is 2017.2.0f2
.net version: tryed to use .net 2.0, .net 2.0 subset and .net 4.5. Had the same result

Guys i found the answer!!!

So after hours of reaserach i give up and tried to solved myself. SO THE PROBLEM WAS TO SIMPLE!!!
You need to download a 32 bits or 64 bitss dll that follows your SO.

Step to glory:

Create a folder in assest called Plugins: unity use this folder to load your external DLLs, if you put here unity install the DLLs automatic, and you just need to add Using yourDLL in your project and it works. If the error “The type or namespace name ‘Data’ does not exist in the namespace ‘System’, are you missing ‘System.data’ assembly reference?” happens just try to download another version (if you tried 32 bits dll try a 64 bits dll)