First of all, thanks for your replies.
I've already tried with:
Notepad++
HxD Hex Editor
VIsual COde Studio

All of these softwares  show me only 75 lines of corrupted code: SCREENSHOT
I've already re-downloaded the files and tried other combinations as you described. Maybe someone can send me the edited file. 
Thanks again

EDIT: I'm just an idiot. I was trying to edit the code inside the BF4DB_API.dll file instead of the BF4DB.cs file.


Everything is perfectly working now.
Thanks for your patience, I'm a noob :D

Good evening, I've already replied on thread but I can't find it anymore.
I've subscribed a plan for a BF4 server  hosted by g-portal.com

I've claimed the server on my profile on BF4DB and got the API, but there's no way to upload the BF4DB_API.ddl  plugin file. 
Already tried to follow these instructions but when i try to edit the file with Visual Studio Code, it shows me only corrupted lines.
How can i solve this?
Thanks and sorry for bad english.