Extract only right most n letters from a string

string SubString = MyString.Substring(MyString.Length-6);

Write an extension method to express the Right(n); function. The function should deal with null or empty strings returning an empty string, strings shorter than the max length returning the original string and strings longer than the max length returning the max length of rightmost characters.

public static string Right(this string sValue, int iMaxLength)
{
  //Check if the value is valid
  if (string.IsNullOrEmpty(sValue))
  {
    //Set valid empty string as string could be null
    sValue = string.Empty;
  }
  else if (sValue.Length > iMaxLength)
  {
    //Make the string no longer than the max length
    sValue = sValue.Substring(sValue.Length - iMaxLength, iMaxLength);
  }

  //Return the string
  return sValue;
}

if you are not sure of the length of your string, but you are sure of the words count (always 2 words in this case, like 'xxx yyyyyy') you'd better use split.

string Result = "PER 343573".Split(" ")[1];

this always returns the second word of your string.

This isn't exactly what you are asking for, but just looking at the example, it appears that you are looking for the numeric section of the string.

If this is always the case, then a good way to do it would be using a regular expression.

var regex= new Regex("\n+");
string numberString = regex.Match(page).Value;