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Some advices:

1. Replace File.ReadAllLines with File.ReadLines — first will read all file content into memory before start, and foreach is really designed to IEnumerable
2. Definetly replace for (int row = 0; row < numbers.Count; row++), for (int j=0; j<rowTotal.Length; j++) and for (int i = 1; i <= iterations; i++) with plinq as @ANeves adviced you before
3. Not sure that replacing foreach (string line in File.ReadAllLines(@"data.txt")) will help you, as it is heavily depend on disc I/O operations.

Some advice:

1. Replace File.ReadAllLines with File.ReadLines — ReadAllLines will read all file content into memory before the iteration, and foreach is really designed for IEnumerable.
2. Definitely replace for (int row = 0; row < numbers.Count; row++), for (int j=0; j<rowTotal.Length; j++) and for (int i = 1; i <= iterations; i++) with PLinq as @ANeves suggested
3. Not sure that replacing foreach (string line in File.ReadAllLines(@"data.txt")) will help you, as it is heavily dependent on disc I/O operations.