I want to show the results of this code in my TextBox:
string txtout1 = txtOrgText.Text.Replace(parm, txtTo.Text).ToString();
txtout = txtout1;
First of all txtout = txtout1;
will not serve as txtout is a textbox and txtout1 is a string .You should use
txtout.Text = txtout1
ie .Text property of textbox says Gets or Sets the current text in System.Windows.Forms.TextBox and its type is string as your txtout1 is already a string there is no need to convert it again by using .ToString()