In case you are wondering why people have downvoted you, it's because you have bastardized the computing usage of 'portable' almost beyond recognition. Word documents are one of the classic examples of unportable file formats - formats locked into Microsoft software, which are portable neither over time nor computing platforms.

Although it might also just be because you are apparently wrong when you say you can't email a PDF to your Kindle like you can your Word documents.

(Even the XML MS format is pretty terrible, as groups like Groklaw analyzed back when MS first began pretending it was a real alternative to OOXML.)