How to reproduce:
public partial class Form1 : Form
{
    RadRichTextBox tb1;
    RadRichTextBox tb2;
    private bool shouldFocus = false;

    public Form1()
    {
        InitializeComponent();

        tb1 = new RadRichTextBox();
        this.Controls.Add(tb1);

        tb2 = new RadRichTextBox();
        tb2.Location = new Point(200, 0);
        this.Controls.Add(tb2);

        this.Load += Form1_Load;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        StyleDefinition style = new StyleDefinition();
        tb1.IsReadOnly = true;
        tb1.Document.Insert("text 1", style);

        tb2.Document.Insert("text 2", style);
        tb2.IsReadOnly = true;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        tb1.IsReadOnly = false;
        tb2.IsReadOnly = false;
        tb1.Focus();
    }
}

Workaround:
public partial class Form1 : Form
{
    RadRichTextBox tb1;
    RadRichTextBox tb2;
    private bool shouldFocus = false;

    public Form1()
    {
        InitializeComponent();

        tb1 = new RadRichTextBox();
        tb1.GotFocus += tb1_GotFocus;
        tb1.LostFocus += tb1_LostFocus;
        this.Controls.Add(tb1);

        tb2 = new RadRichTextBox();
        tb2.Location = new Point(200, 0);
        tb2.GotFocus += tb2_GotFocus;
        tb2.LostFocus += tb2_LostFocus;
        this.Controls.Add(tb2);

        this.Load += Form1_Load;
    }

    private void tb2_LostFocus(object sender, EventArgs e)
    {
        shouldFocus = false;
        tb2.IsReadOnly = true;
    }

    private void tb2_GotFocus(object sender, EventArgs e)
    {
        if (shouldFocus)
        {
            tb2.IsReadOnly = false;
        }
    }

    private void tb1_LostFocus(object sender, EventArgs e)
    {
        tb1.IsReadOnly = true;
    }

    private void tb1_GotFocus(object sender, EventArgs e)
    {
        if (shouldFocus)
        {
            tb1.IsReadOnly = false;
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        StyleDefinition style = new StyleDefinition();
        tb1.IsReadOnly = true;
        tb1.Document.Insert("text 1", style);

        tb2.Document.Insert("text 2", style);
        tb2.IsReadOnly = true;
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        if (shouldFocus)
        {
            tb2.Focus();
        }
        else
        {
            shouldFocus = true;
            tb1.Focus();
        }
    }
}

When the RadRichTExtEditor.Document is rapidly changed not all memory is released

Workaround: 
Point loc = radRichTextEditor1.Location;
Size size = radRichTextEditor1.Size;
radRichTextEditor1.Dispose();
radRichTextEditor1 = new RadRichTextEditor();
radRichTextEditor1.Location = loc;
radRichTextEditor1.Size = size;

this.Controls.Add(radRichTextEditor1);

To reproduce:
- Add comment and try to select the text with the mouse.

Workaround: use keyboard to select the desired text

Workaround: explicitly set the font size of the spans in the heading paragraphs
foreach (Section section in this.radRichTextEditor1.Document.Sections)
{
    foreach (Block block in section.Blocks)
    {
        Paragraph p = block as Paragraph;
        if (p != null && p.StyleName == "Heading1")
        {
            foreach (var item in p.Inlines)
            {
                Span s = item as Span;
                if (s!= null)
                {
                    s.FontSize = p.FontSize;
                }
            }
        }
    }
}

The LocalizeStrings method of the FloatingBlockPropertiesDialog refers to the "Documents_FindReplaceDialog_ReplaceWith" string. This should be "Documents_FloatingBlockPropertiesDialog_TextWrapping"

Workaround:
public Form1()
{
    InitializeComponent();

    FieldInfo fi = this.radRichTextEditor1.RichTextBoxElement.FloatingBlockPropertiesDialog.GetType().GetField("radPageViewPage2", BindingFlags.NonPublic | BindingFlags.Instance);
    RadPageViewPage textWrappingPage = (RadPageViewPage)fi.GetValue(this.radRichTextEditor1.RichTextBoxElement.FloatingBlockPropertiesDialog);
    textWrappingPage.Text = "TextWrapping";
}

To reproduce:
Add image like this:
void button_Click1(object sender, EventArgs e)
{
    Section section = new Section();
    Paragraph paragraph = new Paragraph();
    ImageInline image;
    Telerik.WinControls.RichTextEditor.UI.Size size = new Telerik.WinControls.RichTextEditor.UI.Size(236, 50);
    using (MemoryStream ms = new MemoryStream())
    {
        System.Drawing.Image.FromFile(@"C:\img\delete.png").Save(ms, System.Drawing.Imaging.ImageFormat.Png);
        image = new ImageInline(ms, size, "png");
    }

    paragraph.Inlines.Add(image);
    section.Children.Add(paragraph);
    this.radRichTextEditor1.Document.Sections.Add(section);
}

Workaround:
Manually update the layout:
 this.radRichTextEditor1.UpdateEditorLayout();

To reproduce:
Seth the default font like this:

radRichTextEditor1.Document.StyleRepository[RadDocumentDefaultStyles.NormalStyleName].SpanProperties.FontFamily = new Telerik.WinControls.RichTextEditor.UI.FontFamily("Segoe Script");
          
radRichTextEditor1.RichTextBoxElement.ChangeFontFamily(new Telerik.WinControls.RichTextEditor.UI.FontFamily("Segoe Script"));
radRichTextEditor1.RichTextBoxElement.ChangeFontSize(Unit.PointToDip(12));
radRichTextEditor1.RichTextBoxElement.ChangeFontStyle(Telerik.WinControls.RichTextEditor.UI.FontStyles.Italic);
radRichTextEditor1.RichTextBoxElement.ChangeFontWeight(Telerik.WinControls.RichTextEditor.UI.FontWeights.Bold);

Start the application and insert header footer and endnotes.

To reproduce:
- Create a document in Word and add image watermark to it.
- Open the document in RadRichtextEditor

To reproduce:
- Add RichTextEditorRibbonBar to a form and open it upon button click several times.
- You will notice that the memory is constantly increasing.

Workaround:
protected override void Dispose(bool disposing)
{
    if (disposing && (components != null))
    {
        components.Dispose();
    }

    FieldInfo f1 = this.richTextEditorRibbonBar1.GetType().GetField("tabTableStyle", BindingFlags.NonPublic| BindingFlags.Instance);
    RichTextEditorRibbonTab tab1 = f1.GetValue(richTextEditorRibbonBar1) as RichTextEditorRibbonTab;
    tab1.Dispose();

    FieldInfo f2 = this.richTextEditorRibbonBar1.GetType().GetField("tabTableLayout", BindingFlags.NonPublic | BindingFlags.Instance);
    RichTextEditorRibbonTab tab2 = f2.GetValue(richTextEditorRibbonBar1) as RichTextEditorRibbonTab;
    tab2.Dispose();

    FieldInfo f3 = this.richTextEditorRibbonBar1.GetType().GetField("tabHeaderFooter", BindingFlags.NonPublic | BindingFlags.Instance);
    RichTextEditorRibbonTab tab3 = f3.GetValue(richTextEditorRibbonBar1) as RichTextEditorRibbonTab;
    tab3.Dispose();

    base.Dispose(disposing);
}

Implement support for content controls (a.k.a. Structured document tags), which will allow inserting editing controls in the document:

- Rich Text
- Plain Text
- Check Box
- Combo Box
- Drop-down list
- Date picker

Add similar functionality as MS Word.

To reproduce:
- Start the demo application 
- Type some text and try to make it bold  with the bold button from the ribbon.

Workaround:
void richTextEditorRibbonBar1_MouseDown(object sender, MouseEventArgs e)
{
    radRichTextEditor1.RichTextBoxElement.SelectionMiniToolBar.Hide();
}

If you populate the document with more than one section as shown below:

Section Section1 = radRichTextEditor.Document.Sections(0);
Paragraph Paragraph1 = new Paragraph(); 
Span Span1 = new Span("Thank you for choosing Telerik");
Section1.Blocks.Add(Paragraph1);

Section Section2 = new Section();
Paragraph Paragraph2 = new Paragraph();
Paragraph2.Inlines.Add(image);
Section2.Blocks.Add(Paragraph2);
radRichTextEditor..Document.Sections.Add(Section2);

then mark as selected the space after the first span, then try to type a character, a NullReferenceException will be thrown.

WORKAROUND:

class MyInputBehavior : RichTextEditor.RichTextEditorInputBehavior
{
	public MyInputBehavior(RadRichTextBox editor) : base(editor) { }

	public override void InsertText(string text)
	{
		if (this.RichTextBox.IsReadOnly) {
			return;
		}

		Telerik.WinForms.Documents.UI.CaretTextInputHandler handler = null;

		DocumentPrintLayoutPresenter printLayout = this.RichTextBox.ActiveEditorPresenter as DocumentPrintLayoutPresenter;

		if (printLayout != null) {
			DocumentPagePresenter pagePresenter = printLayout.GetFocusedPresenter();
			if (pagePresenter == null) {
				pagePresenter = ((Canvas)printLayout.Content).Children[0] as DocumentPagePresenter;
			}
			handler = pagePresenter != null ? pagePresenter.CaretTextInputHandler : null;
		}

		DocumentWebLayoutPresenter webLayout = this.RichTextBox.ActiveEditorPresenter as DocumentWebLayoutPresenter;

		if (webLayout != null) {
			handler = webLayout.CaretTextInputHandler;
		}

		if (handler != null) {
			handler.HandleTextInsertedWithoutIme(this.RichTextBox.ActiveEditor.Document, text);
		}
	}
}

radRichTextEditor.InputHandler = New MyInputBehavior(radRichTextEditor.RichTextBoxElement)

To reproduce:
- Add some full pages to the editor. 
- Remove all margin from the print settings and document settings.
- PrintPreview the document.
- Seth the print preview dialog zoom to 100% and compare the documents.
- You will notice that the print document's content is smaller.

To reproduce
Write a word in an RightToLeft language and then type "."
You will notice that the dot is moved to the end of the word.

One should be able to change the document while the Find/Replace dialog is open.

Please refer to the attached gif file.