From Illustrator to png with the help of ImageMagick

Question

Currently I save my files in Illustrator as .pdf files so that I can use ImageMagick to manipulate the resulting images programatically (cropping, adding borders, resizing, etc) and convert them to .png (the format that I eventually need all my images on).

The reason why I edit my files in Illustrator in.pdf as opposed to .ai is because, as far as I understand, ImageMagick does not support .ai directly.

However, when I choose to save an Illustrator file in CS5 as a .pdf file while keeping editing compatibility on, the background seems to lose its transparency, or at least that's what I see when I ask ImageMagick to convert the .pdf file to .png with

mogrify -alpha "on" -background transparent -format .png file.pdf

since I can easily check the transparency on the png file.

So I am wondering two things:

1. Is there a way to directly check if the background on a .pdf file is transparent? This would help me diagnose the problem of losing background transparency in my .png files, since at the moment I have no way of checking if the background transparency is lost in the process of saving Illustrator files as .pdf (as opposed to .ai), or in the conversion from .pdf to .png.

2. As I said earlier, I usually save an my illustrator files in .pdf mostly because I can then use ImageMagick to convert the resulting file to a .png and still keep the ability to make changes on a file that supports Illustrator's objects and features almost natively.

   However, I am wondering if there is a different path to get a .png from an .ai file using ImageMagick while preserving background transparency and the ability to fully edit the original objects in Illustrator.