I am trying to watch an MP4 file (saved on my PC) on my iPad 4. I've done numerous things to add the video to the iTunes library, but it doesn't seem to 'accept' the file, and hence I cannot sync it to my iPad - help please!!!
You need to make sure the mp4 file is within the specs needed by your iPad. Chances are it's either the wrong resolution, bitrate, or codec.
If you're on a mac, Handbrake is awesome for converting files for iPhone or iPad, and has presets built in.