Hi, @camlorn

Thank you very much for your help, it's runing perfectly now.

I paste my code below, could be interesting for someone:
//First, add the corresponding using:
using System.Runtime.InteropServices;

// Then declare the class:
public class screenreader
    {
//use this directive to inport the file located on the same folder of your executable       
[DllImport("UniversalSpeech.dll", CharSet = CharSet.Auto)]
//now, the function itself, inported from UniversalSpeech.dll
        public static extern IntPtr speechSay(string text, bool value);
//your code, etc
}

//last but not least, you can call this method anywhere like that o say a string:
screenreader.speechSay("Hello, world", true);
   
It doesn't use more powerful capabilities on the universalSpeech library, but you can inport any other function just the same way.

Have a nice day,

Alan.