There is some free software available[0] to do stylometry analysis. And some software which purports to assist in anonymizing writings[1]. I've not really played around with either, so I can't speak to their ease of use and/or effectiveness. But it's at least somewhere to start.

[0] http://evllabs.com/jgaap/w/index.php/Main_Page

[1] https://github.com/psal/anonymouth