Possible workaround is to change the document of RadRichTextBox.

Currently RadDocument contains a lot of built-in (latent) table styles, which are always shown in the TableStylesGallery. Introduce API allowing to hide some of them.

All Microsoft Office applications (Outlook, Exchange, Word, Excel) that can produce HTML are creating them with all of the CSS stylings commented with HTML comment, as follows: <style><!-- CSS --></style>
This is a problem as RadRichTextBox's HTML parser does not import the CSS when it is commented like that.

Workaround: Remove the HTML comment from the CSS style tag.

Currently <big> and <small> tags are not supported and the text inside is not imported.

When trying to import a document containing bookmark and BookmarkRangeEnd is after the last paragraph, a StackOverflowException is thrown in IntervalNode while trying to rebuild the document cache. (RadDocumentChildrenCache.RebuildTree()).

The same could be observed if the bookmark end is last in the header/footer, between table cells in the RadDocument body, or when all paragraphs after the bookmark range end are hidden (with vanish property).

Workaround: Detect the problematic annotations and remove them:
foreach (var rangeStart in document.EnumerateChildrenOfType<AnnotationRangeStart>())
{
    if (rangeStart.End == null || rangeStart.End.Parent == null || rangeStart.End.Parent.Parent == null)
    {
        //MessageBox.Show("This indicates a problem.");
        rangeStart.Parent.Children.Remove(rangeStart);
    }
}

Note: Until 2017 R2 SP1 release StackOverflowException is thrown, after this release an ArgumentException should be thrown.

The ImagesDeflaterCompressionLevel and ContentsDeflaterCompressionLevel in the PdfFormatProvider's export settings have 0 for default value instead of -1.

Workaround: Change the settings's properties to -1 explicitly.

Add adorners for selecting table rows, table columns and table cells with single click, similar to the ones in MS Word

The display mode of all fields is changed to Code, so that the export could work correctly and nested fields would be persisted.
Consider optimizing the algorithm, so that fields take less time to be exported.

When paragraph is in list, the user can choose "Set Numbering Value" which will change the appropriate level Starting Index and will create a new list (or continue the previous one).

When a table is on a page different than the first one and user clicks on the thumb for resizing the table row height, wrong value is calculated and passed to the setter of the TableRow's Height property.

This leads to wrong table layout when the document is exported using RtfFormatProvider.

Popups (ImageMiniToolBar and SelectionMiniToolBar) stay on most top (act as if "Always on Top" is set to them) even if they had lost focus. 

Workaround: Attach to LostFocus or LostKeyboardFocus events and hide the toolbar in the handler:
this.radRichTextBox.LostFocus += (sender, e) =>
{
    this.radRichTextBox.SelectionMiniToolBar.Hide();
    this.radRichTextBox.ImageMiniToolBar.Hide();
};

When the tabbed document becomes a dockable window the ContextMenu Icons are no longer visible.

<telerik:RadDocking x:Name="radDocking"> 
 <telerik:RadDocking.DocumentHost> 
  <telerik:RadSplitContainer> 
   <telerik:RadPaneGroup> 
    <telerik:RadDocumentPane Title="Test"> 
     <telerik:RadRichTextBox x:Name="radRichTextBox" /> 
    </telerik:RadDocumentPane> 
   </telerik:RadPaneGroup> 
  </telerik:RadSplitContainer> 
 </telerik:RadDocking.DocumentHost> 
</telerik:RadDocking>

                 

When the user copy-pastes an image from Outlook, it is pasted as an IncludePictureField and visualized as expected. The field code looks like

{INCLUDEPICTURE :image001.png@01D15D16.4FAF0970 \* MERGEFORMATINET}

However, when the fields in the document are updated, the image is no longer shown because of its invalid Uri. In MS Word, when you paste the image, it is directly inserted as image and the field is skipped.

Workaround - remove the field start/ends (in the attachments)

Consider introducing a property in the XAML that allows the user to set whether the gallery should be loaded asynchronously or not in order to handle scenarios in which the TableStylesGallery is not in a contextual tab.

"Win32Exception (0x80004005): Not enough storage is available to process this command" is thrown when multiple RadDocument instances are created in background threads. 

This is due to the fact that RadDocument contains MailMergeDataSource object, which is DependencyObject. When multiple dependency objects are created in different threads, they are not property freed by thread's Dispatcher.

Workaround 1: Microsoft provided workaround in a bug report here:
https://connect.microsoft.com/VisualStudio/feedback/details/620588/system-componentmodel-win32exception-0x80004005-not-enough-storage-is-available-to-process-this-command , namely:
------------------------------
Put the following code:

Dispatcher dispatcher = Dispatcher.CurrentDispatcher;
dispatcher.BeginInvokeShutdown(DispatcherPriority.Normal);
Dispatcher.Run();

anywhere in the background thread processing the RadDocument.
-----------------------------

Workaround 2: Use pooling of the used threads. The problem is that Task Parallel Library (which has built-in pooling) does not use STA threads by default, but this can be achieved by using custom TaskScheduler (attached, the code is get from here: https://code.msdn.microsoft.com/ParExtSamples ):

            var parallelOptions = new ParallelOptions()
            {
                TaskScheduler = new StaTaskScheduler(Environment.ProcessorCount)
            };

            Parallel.For(0, 10000, parallelOptions, cc =>
            {
                    var document = new DocxFormatProvider().Import(data);
                    byte[] pdfBytes = new PdfFormatProvider().Export(document);

            };

According to the RTF Specification, each bookmark start should have a matching bookmark end. However, when opening a document which contains bookmark start without bookmark end, MS Word treats the start position for an end as well and successfully opens the document. When such document is being imported in RadRichTextBox, an InvalidCastException is thrown.

This causes some problems if the hyperlink is edited and the document is exported and imported again.
Workaround:
private void RadRichTextBox1_DocumentChanged(object sender, EventArgs e)
{
    var document = radRichTextEditor1.Document;

    var fields = document.EnumerateChildrenOfType<FieldRangeStart>();

    foreach (FieldRangeStart item in fields)
    {
        radRichTextEditor1.DeleteAnnotationRange(item);
    }
}

This element specifies a set of table properties which shall be applied to the contents of this row in place of the table properties specified in the tblPr element.

When importing an image, defined with a Base64 string which doesn't have its size explicitly set, it is rendered with ImageInline.DefaultImageSize instead of using its real size.

Workaround: Check the size defined in the ImageSource:

The built-in Hyperlink style is not applied to hyperlinks imported from HTML (<a> tag). As a result, the hyperlinks in the document do not have the blue underline.

Workaround: Subscribe for the SetupDocument event of the HtmlDataProvider and set the hyperlinks' style manually.
private void HtmlDataProvider_SetupDocument(object sender, Telerik.Windows.Documents.FormatProviders.SetupDocumentEventArgs e)
{
    StyleDefinition hyperLinkStyle = e.Document.StyleRepository[RadDocumentDefaultStyles.HyperlinkStyleName];
    hyperLinkStyle.SpanProperties.ForeColor = Colors.Green;//Color.FromRgb(0xff, 0x7a, 0xcc);
    var hyperlinks = e.Document.EnumerateChildrenOfType<HyperlinkRangeStart>();

    RadDocumentEditor editor = new RadDocumentEditor(e.Document);
    editor.Document.History.IsEnabled = false;

    foreach (HyperlinkRangeStart hyperlink in hyperlinks)
    {
        e.Document.Selection.SelectAnnotationRange(hyperlink);
        editor.ChangeStyleName(RadDocumentDefaultStyles.HyperlinkStyleName);
    }
    e.Document.Selection.Clear();

    editor.Document.History.IsEnabled = true;
}