C#

How can I implement NLP in c# program? Is there any logic for extracting single/multiple words from one or more sentences?
For more understandability, I included a paragraph(Doctor's Note) here.

The patient x is suffering from fever. He has no headache, cough or neck pain. But he has back pain.
Moreover patient x suffers Sleeplessness.

 
<big>My requirement is</big>,
 I need to iterate symptoms such as <big>fever, back pain and sleeplessness</big>. And 
do not take symptoms <big>headache, cough and back pain</big> .

using System;

public interface IStuff
{
   void SPB(string a, DateTime d, string c);
   void P(decimal a, string r);
   void EPB();
}

using System;

namespace Namespace1
{
    public class Stuff : IStuff
    {
        public void SPB(string a, DateTime d, string c)
        {
        }

        public void IStuff.P(decimal a, string r)
        {
        }

        void EPB()
        {
        }
    }
}

public void IStuff.P(decimal a, string r)
{
}

public void P(decimal a, string r)
{
}