Question: I am using a RichTextBox in WPF, and am trying to set the default paragraph spacing to 0 (so that there is no paragraph spacing). While I could do this in XAML, I would like to achieve it programmatically if possible. Any ideas?

Answer: 
Using Line Height

```
RichTextBox rtb = new RichTextBox();    
Paragraph p = rtb.Document.Blocks.FirstBlock as Paragraph;    
p.LineHeight = 10;

```
For me on VS2017 in WPF works this:

```
 <RichTextBox HorizontalAlignment="Left" Height="126" Margin="10,280,0,0" VerticalAlignment="Top" Width="343" FontSize="14" Block.LineHeight="2"/>

```

The key is **Block.LineHeight="2"**

You can found this also in Properties view but you can't change below 6px from there.