PHP Generate preview of Microsoft formats

I've made in PHP (using GD and Imagick) a image preview generator for jpg, gif, png, bmp, t开发者_如何学JAVAxt, csv and pdf files, but I'm having troubles on finding a solution for Microsoft types: doc, xls and ppt.

Anyone has some ideas on how to generate them?

http://code.google.com/intl/el-GR/apis/books/docs/viewer/developers_guide.html http://blogs.digitss.com/tools-plugins-extenstion/use-google-docs-viewer-for-document-viewing-within-browser/

I think that these formats are proprieraty.. Check google viewer or search for another solution..