DLL files reverse engineer, Plugin for Revit

Sorry for posting in english, unfortunately I don’t speak russian.
I’ve been trying to reproduce the functionality of a plugin for the construction program Autodesk Revit but i’m not so good at programing so i thought to reverse engineer the plugin and peek into how it works.
I’m attaching the whole plugin folder - http://www.mediafire.com/file/vna3l4avz5gy46q/2018.1.zip
The main software - Revit - opens first this file: GraitecRevitDesign.dll, this produce the following tab:

What i’m interested in mainly is the code associated with the button Bending Detail which produces an annotated detail for reinforcement bars.
I believe that the methods associated with this button are in GraitecRevitReinforcementTools.dll. Anyway if someone could help me decompile the dll i will look over to find the exact code. I’m not sure if the software was written in visual C++ or C#.

Although I’ve no experience in reverse engineering, I tried to use multiple software like dotPeek, ILSpy, dnSPy, de4dot (to try deobfuscating) but i only get this type of errors:

If someone will be willing to help me out I can send a reward in btc, eth or ltc. Thank you!