Instead of this:
<TextBlock Text="Hello
How Are
You??"/>
Use this:
<TextBlock>
Hello
How Are
You??
</TextBlock>
or this:
<TextBlock>
<Run>Hello</Run>
<Run>How Are</Run>
<Run>You??</Run>
</TextBlock>
or set Text property in code behind like this :
(In XAML)
<TextBlock x:Name="MyTextBlock"/>
(In code - c#)
MyTextBlock.Text = "Hello How Are You??"
Code-behind approach has an advantage that you can format your text before setting it. Example: If the text is retrieved from a file and you want to remove any carriage-return new-line characters you can do it this way:
string textFromFile = System.IO.File.ReadAllText(@"Path\To\Text\File.txt");
MyTextBlock.Text = textFromFile.Replace("\n","").Replace("\r","");