Thank you for contacting us!
Unfortunately, this will not be possible with the current implementation of RadPdfViewer and is not in our development plans. Though changing the font of PDF files is possible, it contradicts with the general idea of the files being application independent. Also, not all fonts contain all characters and such conversion might cause unwanted results. We might reconsider introducing a way to achieve similar results in the future, but for now I cannot engage with any time-frame.
Let us know if you have other questions.