In "D10" the "D" is the format specifier which in this case is decimal. The "10" is the precision specifier which is the minimum number of digits in the result and is normally padded with zeros to the left to produce the number of digits given by the precision specifier.
Code:
using System;
public class George2
{
public static void Main()
{
int value = 12345;
Console.WriteLine(value.ToString("D"));
Console.WriteLine(value.ToString("D10"));
value = -12345;
Console.WriteLine(value.ToString("D"));
Console.WriteLine(value.ToString("D10"));
}
}
Output:
12345
0000012345
-12345
-0000012345