You can use the Adobe Media Encoder (comes with Creative Suite and Creative Cloud) to convert to MP4.
I was able to upload quick time movies (.mov) into the pdf – the movies were professionally made.
When I share and save the file in different formats like mpeg, windows media and quick time, they save as Adobe Premiere Elements Project (.prel) files; making them unable to import.
There has to be something little that I am doing wrong, but I cannot figure it out!
I'd suggest asking on the Premiere Elements forum. It's not something we really can help with here.