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I suppose that the reason the text is not displayed correctly is that the fonts used in this documents are not embedded in it according to specification due to a Silverlight limitation. Most viewers seem to resolve the fonts from the OS, but if they are missing on the Apple device you might experience the mentioned behavior. In order to solve this issue, the fonts should be embedded in the document for example by generating the PDFs with the WPF version of RadRichTextBox in a service.
I hope this helps. Don't hesitate to contact us if you have any other questions.
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