Copying Sketchbook Pro sketches to computer

I have 7GB of sketches on my iPad. I would like to remove most of them from the app and store them on my computer. However, I've downloaded two different file explorers and for both, only drawings that were exported to iTunes show up under the documents folder in the app. I need a way to copy about 6gb worth of sketches to my computer and then to delete them out of the app. My iPad has 0bytes of space remaining so I cannot do any solutions that involve using any more space on there. I'd prefer not to do it manually, as that would take hours.