Creating deep copy using CreateDeepCopy method of an empty Section (without paragraphs or with one empty paragraph) adds empty string Span which leads to ArgumentOutOfRangeException. 

Workaround: clear the empty string Spans before measuring:

foreach (Span span in sectionClone.EnumerateChildrenOfType<Span>().ToList())
{
    if (string.IsNullOrEmpty(span.Text))
    {
        ((Paragraph)span.Parent).Inlines.Remove(span);
    }
}




Steps to reproduce:

1. Execute the following code-snippet:

RadDocument document = new RadDocument();
Section section = new Section();
section.Blocks.Add(new Paragraph());
document.Sections.Add(section);

RadDocument documentClone = (RadDocument)document.CreateDeepCopy();
Section sectionClone = (Section)section.CreateDeepCopy();
documentClone.Sections.Clear();
documentClone.Sections.Add(sectionClone);
documentClone.EnsureDocumentMeasuredAndArranged();

2. Set the documentClone to a RadRichTextBox instance to visualize it.

3. Try to click in the document.

Observe: ArgumentOutOfRangeException is thrown.