How to display m² in pdf using pdf sharp?

I need to create and download pdf. In pdf sharp, it only display characters which are on our keyboard the characters typing with the help of alt key cannot be displayed and shows object reference not set to an instance error. If I check condition:
if(a.contains("²")
{
//replace with 2
}
works fine. But ² cannot be 2. I am stuck on that. Please help me.