In case that DearMob iPhone Manager could not satisfy your needs, you can refer to these kinds of EPUB to PDF converters to convert EPUB to PDF if you don't mind that some of them are difficult to use or not authentic, and some of them also require you to register first.
1. Convert M4V to MP4 on Mac using Requiem
The harsh fact about Requiem is that it only works with iTunes 9.0.2 or earlier and it is incompatible with Mac OS X 10.9 or above. Requiem upgrade has stopped since 2012.
2. Convert M4V to MP4 on Windows using TunesKit
A good thing about TunesKit is that it doesn't perform a re-encoding of the movie but just leaves unchanged the video and audio tracks by removing all DRM protection only. This means you can get a lossless M4V to MP4 conversion. The not-so-good part about this software is that it takes $49.95 with only the ability to remove DRM.
3. Convert M4V to MP4 using NoteBurner M4V Converter
This M4V Converter converts M4V differently from TunesKit since it gives you a 1:1 copy rather than just striping DRM from M4V file with original tracks retained. Quality loss is to some extent unavoidable. And its price does not get any cheaper than TunesKit, at $49.95 also.