Automatically convert a file whenever it is saved?
Yes, OS X has built in automation with Applescript and folder actions.


http://www.macworld.com/article/1167157/automate_tasks_with_folder_actions.html
http://apple.blogoverflow.com/2012/06/folder-actions-tutorial-automation-meet-the-filesystem/
https://developer.apple.com/library/mac/documentation/AppleScript/Conceptual/AppleScriptLangGuide/reference/ASLR_folder_actions.html
https://developer.apple.com/library/mac/releasenotes/InterapplicationCommunication/RN-JavaScriptForAutomation/index.html
http://macosxautomation.com


So, following the first link from MacWorld you can make a folder on your desktop that pops up an alert when you save your file. From there, you would make a different folder with a different script to attempt to convert the file. Lastly, make a script to clean up the file that's converted and move the processed file to the proper place.

I would instead make a service to just convert the file in place, but you can't trigger a service as easily as you can trigger a folder based workflow where actions initiate the processing.