Sorry for not being able to reply sooner. I don't seem to get an email alert of your message which delayed the response.
We are investigating the issue with using this web part on Master and will let you know our findings. Yes the initial version of the web part converts the page as a whole, however we have planned to allow users to select area before exporting in the next version.
The web part itself is free and open source however it uses Aspose.Words for .NET in the back-end to generate the exported document which is a commercial product, evaluation versions with time restricted limitations are available for use with this plug-in. Terms and conditions apply.
Please feel free to reach out if you have more questions.
Have a nice day