using System;

using System.Collections.Generic;

using System.Text;

​

public static class Program

{

    public static string basetext="Hi, this is ##### reaching out to you to get the information about #####. Please call us at ##### for more information";

    public static void Main()

    {

        List<int> indexes = basetext.AllIndexesOf("####");

        string newstring = basetext;

        var aStringBuilder = new StringBuilder(newstring);

        for(int i=indexes.Count -1 ;i>=0;i--)

        {

        aStringBuilder.Remove(indexes[i],5);

        aStringBuilder.Insert(indexes[i],"<input type='text' id='Item'"+i.ToString()+" style='font-weight:600;width:100px;border-top:white;border-right:white;border-left:white;text-align:center' />");    

        }

        Console.Write(aStringBuilder.ToString());

    }

​

    public static List<int> AllIndexesOf(this string str, string value)

    {

        if (String.IsNullOrEmpty(value))

            throw new ArgumentException("the string to find may not be empty", "value");

        List<int> indexes = new List<int>();

        for (int index = 0;; index += value.Length)

        {

            index = str.IndexOf(value, index);

            if (index == -1)

                return indexes;

            indexes.Add(index);

        }

    }

}