Search and replace contents of text file based on mappings in CSV fiile in C#
===

I am new to programming and am working on a C# project that will search and replace certain words in a text file with new values.  I have some code that works, but the OLD and NEW values are hardcoded right now.  I would like to use a external CSV file as a config file so the user can add or update the OLD to NEW mappings at a later time.  This is my current code with the OLD and NEW values hardcoded:

         try
         {
            StreamReader file = new StreamReader(inputfullfilepath);
            TextWriter writer = new StreamWriter(outputfile);
 
          
                while ((line = file.ReadLine()) != null)
                {
                    line = line.Replace("OLD1", "NEW1");
                    line = line.Replace("OLD2", "NEW2");
                    // etc....
                     
 
                    writer.WriteLine(line);
                   }
                file.Close();
                File.Move(inputfullfilepath, inputfullfilepath + ".old");
                writer.Close();
                File.Move(outputfile, outputfilepath + @"\" + inputfilename);
                MessageBox.Show("File Scrub Complete", "Success");
            }
            catch
            {
                MessageBox.Show("Error:  Be sure data paths are valid.", "Error",                 MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }

The code takes each line of the text file, tries to do a search/replace for all OLD to NEW mappings, then goes to the next line in the text file.  The problem I am trying to wrap my head around is being able to make this list of OLD to NEW mappings dynamic based on a CSV (or XML if that would be easier?) config file so the user can add new search/replace keywords.  

I tried to use the C# Application Settings in VS (which creates an XML config file) but I had a really hard time understanding how to make that work.  What's the best way to do this so the values don't have to be hardcoded?