Fulfilling a common request for new APIs, Windows 8.1 adds a PDF rendering API that’s found in the Windows.Data.Pdf namespace and demonstrated in the PDF viewer sample and the more extensive PDF viewer showcase sample. The API itself can open and load PDFs, then you request that individual pages be rendered to a stream. That stream can then be turned into a graphic for whatever UI framework you’re using. The //build talk is Rendering PDF Content in Windows Store Apps (3-175).
Windows 8.1 also adds a text-to-speech API, which you’ll find in Windows.Media.SpeechSynthesis and demonstrated in the Speech synthesis sample. The //build talk on this is Making Your Windows Store Apps Talk (2-171).
Speaking of text, also look at the Windows.Data.Text namespace, where there’s a bunch of new stuff for text segmentation and Unicode. There are some related samples, but I haven’t worked through those enough yet to comment further.