Many users want to play the iTune M4P files on their MP3 player or mobile phone etc, but the files which downloaded from iTune store was DRM protected, I know you can download the DRM free M4P files from iTunes Plus, but not all of the music provide DRM free version, and it may cost your a bit money. Why you don't convert M4P to MP3 directly? What you need to do just two steps:
1.Download and Install Tunebite Platinum. You could download here.
2.Convert the M4P files to MP3 on Tunebite Platinum.
This step by step guide will teach you how to do that, let’s start it.
Step 1. Download and install Tunebite Platinum. Located your iTunes purchased music or movies on your computer; after you purchased movie or TV shows from iTunes online store, you should find the downloaded movie in the iTunes install folder. And then run the Tunebite and click “Add -> Add files” to import your iTunes M4P Files.

Step 2. Select the format which you want convert to, Tunebite not only convert DRM protected M4P to MP3, but also OOG, WMA and M4A, and you could convert DRM protected movies and videos.

Step 3. Press the Start button to start the M4P to MP3 Conversion.

Done.