You do not need any software for that. You can just use your device email service to convert. Plus, I think Kindle email convert service is more successful than the Calibre in converting multi-column Pdf's.
How to do: Just email one pfd file to your Kindle mail account [email protected] (every kindle owner has such an email address given by Amazon, you could find in your device "Settings - Device Options - Personalise Your Kindle - Send-to-Kindle E-mail").
Note that: The subject of the email needs to be "Convert"The subject of the email needs to be "Convert"
Otherwise: It is not converted and placed in your device as a pdf file.
