For example, if the document has "Times New Roman" as a default font family, the "TableNormal" style doesn't have set that property and there is a Table element in the header - the value is not properly obtained ("Verdana" is applied, which is the default value for that Span property).
The problem is observed for all default span style properties.

Workaround: Change the table style by setting the necessary properties from the default style. For example for the font family:

object documentFontFamilyPropertyValue = this.radRichTextBox.Document.Style.GetPropertyValue(Span.FontFamilyProperty);
foreach (StyleDefinition tableStyle in this.radRichTextBox.Document.StyleRepository.Where(s => s.Type == StyleType.Table && s.BasedOn == null))
{
    StylePropertyBase styleProperty = tableStyle.GetProperty(Span.FontFamilyProperty);
    if (styleProperty.ValueSource == RadValueSource.Default)
    {
        tableStyle.SetPropertyValue(Span.FontFamilyProperty, documentFontFamilyPropertyValue);
    }
}

In MS Word, images can have strikethrough formatting. In RadDocument's model, this is property of Spans only.

When trying to export a document containing InlineUIContainer inside a read-only range, the XamlWriter.Save() method that is used in XamlFormatProvider.Serialize() throws StackOverflow exception.

Sample code to reproduce the exception:
InlineUIContainer container = new InlineUIContainer();
Button btn = new Button();
btn.Content = "Sample Button";
btn.Width = 70;
btn.Height = 30;
container.UiElement = btn;

ReadOnlyRangeStart start = new ReadOnlyRangeStart();
ReadOnlyRangeEnd end = new ReadOnlyRangeEnd();
end.PairWithStart(start);
this.rtb.InsertInline(container);
this.rtb.Document.Selection.SelectAll();
this.rtb.InsertAnnotationRange(start, end);

XamlFormatProvider provider = new XamlFormatProvider();

string content = provider.Export(this.rtb.Document);
File.WriteAllText(@"c:\temp\asd.xaml", content);

As a user, I'd like to have a way to determine what document elements or layout boxes are in the view port. I may need them in order to:

- Modify something else in the UI depending on them. For example, if a hyperlink or bookmark is scrolled in the viewport, enable buttons outside RichTextBox that execute specific actions.
- Implement formatting changes to the visible elements only in scenarios like a code editor.

Right now, the only way to obtain the visible boxes is to implement a UI layer, however, layers are intended for scenarios in which you'd like to modify the presentation of the control's content and may not be a good idea to utilize them for formatting changes or other actions.

When RadRichTextBox (in Paged layout mode) is in RadTabItem in RadTabControl, ribbon UI buttons and keyboard bindings are not working.

Workaround: Use System's TabControl instead of the RadTabControl.

I have tried to use the RichTextBox, but found that it does not work very well when it comes to measure the text. This results in clipped text and that the caret can be displayed in a different place then expected.
This can easily be seen with a font like Gabriola, which uses complex kerning metrics. Type a text with a lot of "ff" and "fi" and you will soon see that your caret gets out of sync and that text is sometimes clipped.
When I look at the code of RichTextBox it seems to me that it uses its own calculation of text widths and that the this is based on a very simple method using just the kerning information. There is also a hard coded list containing information which fonts that has kerning info and which fonts that are mono spaced. It seems strange to me to have this in a config file since there is a large number of fonts used by the users.
It also seem to look at the Unicode character family in order to determine if ligatures are used or not, which is also quite strange since ligatures can be used for western characters too. The font Gabriola is an example of this. Look at "fi" in a word like "fine".
It can potentially consume a lot of memory since I think that it builds a dictionary of the kerning of all pairs of characters for all fonts that it encounters.
I guess this way of doing things were made for performance, but unfortunately, good performance doesn't help much if it doesn't work.
I am not sure if I should report this as a bug, since it is more of a fatal design issue of the whole control.

please add shapes support for radrichtextbox. else support another textbox

Scroll to the necessary value the vertical offset of the RadRichTextBox if header/footer is not in the viewport, but the editor goes into it.

Workaround: In the current implementation this could probably be achieved by using the ScrollToVerticalOffset method, but the calculations which should be done for the offset value might be not so straight-forward and easy to make. Here is a sample example of this:

this.radRichTextBox.ActiveDocumentEditorChanged += (s, e) =>
{
    if (e.DocumentEditorType == Telerik.Windows.Documents.UI.DocumentEditorType.Footer)
    {
        Section section = this.radRichTextBox.Document.CaretPosition.GetCurrentSectionBox().AssociatedSection;

        double offset = this.radRichTextBox.VerticalOffset + (section.PageSize.Height - section.ActualPageMargin.Bottom) * this.radRichTextBox.ScaleFactor.Height;
        this.radRichTextBox.ScrollToVerticalOffset(offset);
    }
};

While typing in a document containing a table with nested table, and the table is moved to the next page because of the flow of the text, NullReferenceException is thrown. 

When such document is loaded in RadRichTextBox a NullReferenceException could be thrown depending of the exact document or the application will hangs (goes to infinite cycle during the document layout).

Available fix in LIB version 2017.1.410.

Importing HTML with "a:link" CSS style will be applied to the text in a bookmark. Here is example of such HTML:

<html>
  <head>
    <style type="text/css">
      a:link {
        text-decoration: underline;
      }
    </style>
  </head>
  <body>
    <a name="anchor">Anchor element</a>
  </body>
</html>

A possible workaround is to select the content between the bookmarks and apply different underline decoration. Here is example of how this could be done:

List<BookmarkRangeStart> bookmarks = document.EnumerateChildrenOfType<BookmarkRangeStart>().ToList();
foreach (var rangeStart in bookmarks)
{
    document.Selection.Clear();

    var start = new DocumentPosition(document);
    start.MoveToEndOfDocumentElement(rangeStart);

    var end = new DocumentPosition(document);
    end.MoveToEndOfDocumentElement(rangeStart.End);

    document.Selection.AddSelectionStart(start);
    document.Selection.AddSelectionEnd(end);

    RadDocumentEditor editor = new RadDocumentEditor(document);
    editor.ChangeUnderlineDecoration(UI.TextDecorations.DecorationProviders.UnderlineTypes.None);
}

document.Selection.Clear();

Words containing apostrophes are not recognized by the spell checker. Examples: 
- Some contracted forms , for example "they've"
- A lot of common French words, e.g. "Aujourd’hui", "qu’une", "n'est"

The issue could be observed for the single straight (') as well as for the smart (’) quote.

Workaround:
Add the all word parts to the dictionary, for example, to recognize "they've", both "they" and "ve" should be added to the dictionary.

Fix available in LIB Version 2017.3.1009.

Add support for lower-alpha and upper-alpha.

This functionality is not supported out-of-the-box. However, it could be implemented by the users as demonstrated in the Custom Code Formatting Language SDK example (https://github.com/telerik/xaml-sdk/tree/master/RichTextBox/CustomCodeFormattingLanguage).

When editing header/footer in MS Word, the paragraph which is inserted there has defined tab stops. In RadRichTextBox there isn't and thus, when the tab is pressed, a default tab stop is inserted.

Line break has a specific property which should be taken into account only when there is a floating object which interrupts the line, e.g.:

<w:br w:type="textWrapping" w:clear="all" /> 

The width of the table cell is calculated wrongly when it is set in the CSS style and through attribute: <td style="WIDTH: 75%" width=450>First cell</td>. The Unit isn't reset while reading the attribute value as its unit is missing and it is interpreted as % because the previous value is in percent.

Importing HTML document with white spaces and new lines separating the HTML elements will lead to additional intervals between words.

When a document has some section properties like orientation or page size and the document is printed with virtual printer, the generated PDF does not preserve the section properties. 

For example, if the document has Landscape orientation set, in the generated PDF file, the page with Landscape orientation is visualized with Portrait orientation and the text is drawn vertically.
If the document has some page size set, for example A5, in the generated PDF file, the page with size A5 is visualized as page with A4 page size.