Thank you for contacting us.
The issue you are observing is related to a Silverlight limitation which prevents fonts from being embedded in the generated PDF.
What I could suggest as a workaround is to try exporting your documents server-side using the WPF version of RadRichTextBox where the mentioned limitation is not present.
The reason why the document is opening correctly when you open it in new tab is because the browser uses a different viewer which has access to the system fonts which allows the document to be loaded correctly.
If you have further questions or some other concerns do not hesitate to contact us again.
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