1) If you are talking about PWS Cloud conversion service (http://www.pdftron.com/pws/cloud/), then you can find REST API documentation here: http://api.pdftron.com/v2/docs/index.html2) WebViewer doesn't support zip files. You would have to implement that yourself. Please note, XOD is already a ZIP compressed file and doesn't require additional compression.
3) There is no sample, since there are multiple approaches to handle this problem and most of them involve server component. You can learn more about ways to handle CORS problem here: https://groups.google.com/d/msg/pdfnet-webviewer/mtdZAC7mpc8/PbpvFbtSIfEJ