using System;
using System.IO;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var s = "1 2 obj\rObj1\rendobj\r2 3 obj\rObj2\rendobj\r3 45 obj\rObj3\rendobj";
        var matches = Regex.Matches(s, @"(?<=\r|^)(?<obj>\d+ \d+) obj\r(?<objData>.+?)\rendobj(?=\r|$)",
               RegexOptions.Multiline | RegexOptions.Singleline);
        foreach (Match m in matches)
        {
        	Console.WriteLine("___ MATCH ___");
        	Console.WriteLine(m.Value);
        }
	}
}