using System;
using System.Text.RegularExpressions;
using System.Text;
 
public class Test
{
	public static void Main()
	{
		string pattern = @"<\w\w:Value> SYMBOL: (P[^=\n]*)=(.*?)//(.*(?:\n[\p{Zs}\t]*//.*)*)";
        string input = @"<AC:Value> SYMBOL: PDWFNA     = 0;        // Projektierung D-Weg Freimeldung nicht
                                        // auswerten
<AC:Value> SYMBOL: PDWLE      = 0;        // Länge des Durchrutschweges"; 
 
 
        foreach (Match match in Regex.Matches(input, pattern))
        {
            Console.WriteLine(Regex.Replace(match.Groups[3].Value, @"\r?\n[\p{Zs}\t]+//",""));              
        }
	}
}

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