Thank you for using Syncfusion Products.At present we do not have any support for Doc or PDF viewer in Windows Phone. We have already logged feature request for this, we will let you know once this feature is implemented.
We are glad to inform you that we have implemented Doc viewer(SfRichTextBoxAdv control) in our 2014 Volume 4 release. Please find the documentation link for this below.
At Present we do not have a Support for PDF Viewer in Windows Phone 8.1. A support incident to track the status of this feature has been created under your account. Please log on to our support website to check for further updates.
Please let me know if you have any questions.