RadRichTextBox is designed and tested to handle relatively large documents, for example up to 500 pages rich-text content. However even though all UI is virtualized
there are certain document elements that may affect the overall performance. For example if the document contains a lot of tables, annotations, read-only ranges, floating objects, single large paragraphs or even large number of hyperlinks can decrease the performance. Also performance depends on how large is the view-port of the control, is it scaled and what kind of layout mode is used.
With that said we would like to know more about your scenario before we can answer your question more precisely. Can you please elaborate a bit more? And if possible it would help us a lot if you can send us a document so we can first-hand-test the performance. You can open a support ticket to do that.
Anticipating your response.
the Telerik team