To reproduce: - add a RadRichTextBox and use the following code RadDocument document = null; HtmlFormatProvider provider = new HtmlFormatProvider (); OpenFileDialog openDialog = new OpenFileDialog(); openDialog.Filter = "Documents|*.html"; openDialog.Multiselect = false; DialogResult dialogResult = openDialog.ShowDialog(); if (dialogResult == System.Windows.Forms.DialogResult.OK) { using (FileStream stream = new FileStream(openDialog.FileName, FileMode.Open)) { document = provider.Import(stream); } } this.radRichTextBox1.Document = document; Note: in the html file use the following way of commenting the style tag: <style> <!-- some style content --> </style> Workaround: use the following way of commenting the content: <!--<style> some style content </style>--> Resolution: This issue is addressed in the new version of the control - RadRichTextEditor. Please use the new control instead the RadRichTextBox.