StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < originalString.Length; i++)
{
if ((originalString[i] >= 'a' && originalString[i] <= 'z') ||
(originalString[i] >= 'A' && originalString[i] <= 'Z') ||
(originalString[i] >= '0' && originalString[i] <= '9'))
{
stringBuilder.Append(originalString[i]);
}
else
{
stringBuilder.AppendFormat("%{0:X2}", (int)originalString[i]);
}
}
string result = stringBuilder.ToString();