How can I make an automatic blank box out of a text?

I am new to C# and trying to figure out how I could do this. So, what I am trying to do right now is to make a textbox out of text like this. If I have a sentence saying "Hello World. I have a problem. Can you help me?", I want to randomly pick one word and let the user fill it in. Could you please help me how to randomize the pick and make a textbox?

Thanks in advance for your help! :)

PS. I posted a pic for better understanding

Example picture of what I want to do