That's why GoodReaderUSB is so awesome for non-jailbroke iPads. Anything you can get into Goodreader, you can get off with GoodReaderUSB.
For example, I have an epub e-book. Goodreader can't read epubs. But, I can use Goodreader to access Dropbox, download the epub and then use GoodReaderUSB to put it on the PC.
And it's fast! Took that long [snaps fingers] to copy a 25.6 megabyte MP4 video from my iPad to the PC just now. Even faster to delete the video (on the iPad) now that I'm done testing...
Oh, and the Goodreader app does not have to be open on your iPad for GoodReaderUSB on your PC to "see" the files in it.
Note that you can do file transfers wirelessly with Goodreader, also, they are just s--l--o--w. Best to use the USB cable...
Marilyn
[Who is mad at herself for forgetting about how easy GoodReaderUSB is for transfering files back and forth... Thanks, NickHillUK, for reminding me of it!]