Stretching the text is done by modifying the Scale Property of the Character Spacing properties. In the Office Open XML specification, it is represented by the <w:w w:val="300"/> tag. 

InsertTableRowAbove/Below and DeleteTableRow commands now are disabled when there is selection. This makes them inconvenient for the following scenarios:
- Insert multiple rows
- Delete multiple rows

Also, when multiple rows are selected and InsertTableRowAbove/Below is executed, is should add the same number of rows.

Export the image rotation properties to HTML with the CSS transform property (https://developer.mozilla.org/en-US/docs/Web/CSS/transform ).

Enable import/export of read only ranges (protected parts of the document) from/to Rtf documents. 

Implement the export of notes (footnote, endnote) in the PdfFormatProvider of the RadRichTextBox.

In MS Word, Heading and the subsequent paragraphs could be collapsed using a small arrow next to the heading. 

This is not preserved in the model.

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" /> 

Currently, StylesGallery and TableStylesGallery cannot be resized. Internally they contain RadRibbonGallery, which itself expose ViewPortWidth property controlling the width, so this just have to be exposed.

Adding a custom list could be done by using the AddCustomListStyle method of RadDocument. However, this operation will not be included in the Undo stack.

Deleting the full chain of relationships between a list style and a document list is not possible.

It would be more user-friendly if the currently edited word (the one containing the caret) is excluded from the real-time spell checking and, if incorrect, is not underlined until the caret leaves the word boundary. Otherwise currently edited word is marked as incorrect while its typing is still in progress.

Changes in a word can immediately mark it as correct (i.e. to remove the red underline), but cannot mark it as incorrect - it's marked as incorrect only after the caret leaves the word.

When a document is edited by more than one user with enabled Track Changes, there should be an option to show the changes of a certain or multiple users and hide the rest.

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.

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).

In MS Word, for example, when you "Save as" PDF, you can choose "options" -> Encrypt the document with a password.

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);
    }
};

With the current implementation, when an image is selected, viewport is scrolled to the corresponding image document position:

- In case of inline image, it moves to the end of the image, so that the image is fully visible.

- In case of floating image, it moves to the position where image is anchored.

The behavior of the MS Word (the view is not scrolled in such cases) is much more convenient.

Allow Span to be hidden when visualizing the document. For example, introduce a Span.IsHidden property.

In MS Word, text is hidden using the Home -> Font -> Font -> Effects -> Hidden. In the RTF format, such text is preceded (marked) with a '\v' tag. In OOXML, the tag is <vanish/>

Note: Hidden text is visualized with dotted underline when formatting symbols are shown. Hidden text is not exported to PDF.

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.

Implement a Page Setup dialog which allows the users to modify Margins, Layout, Page Size, etc. of the document. 

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