I cannot access richTextBox1.Document which I need for storing into db

Question

I have a Windows Form (.NET Framework) with a rich text box and I want to store its data to a database. Through my research, the code I found was:

string rtfText; //string to save to db
TextRange tr = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
using (MemoryStream ms = new MemoryStream())
{
    tr.Save(ms, DataFormats.Rtf);
    rtfText = Encoding.ASCII.GetString(ms.ToArray());
}

When I try to add line 2 to my code, I get to richTexBox. but Document cannot be found when I type it.

Now when I added a reference, I selected PresentationFramework, and at the top of my code, added the line:

using System.Windows.Documents;
using System.Windows.Controls;

 and I still cannot access richTextBox1.Document. I'm using Visual Stusio 2019 and am using .NET Framework 4.7.2.

 

How can I access  richTextBox.Document?

 

Thanks for the help,

 

Bob Gatto