To reproduce the problem create new blank Word document (from MS Word). Hold Alt key and type 0268. You will see a letter Č (Latin letter C with caron). In Visual Studio create a Word-inspired project, and run it. Copy the text from Word document to the Telerik RTF editor. Now in Telerik RTF editor change the font of this letter to Algerian. I have Algerian font with my Office 2013, so I hope you'll have it too; you can use Symbol font instead of Algerian for the same result. My Algerian font does not support letter Č, so in Telerik RTF editor I will see a narrow empty box (also called "tofu") instead of letter Č.