Originally Posted by travger
Thank you for the great plugin!
I so second the post that said mobi=prc. Why only mobi?
PRC can actually contain many things, as it's originally a PalmOS extension/container format. Anyway Calibre looks inside the PRC container during import and if it's really a mobi file it changes the extension to mobi. If you have prc files in your library that are actually mobi it's because you imported these with a really old version of Calibre.