I'm using the mobile pro edition, (cheaper than the tablet pro edition), and when I open the inbuilt gallery, I can tap on the drawings to edit them, but not select them to export, delete or duplicate them. If I long-press on a drawing it will do nothing until I let go, then it will open for editing g as if I had tapped it.
That's the usual behaviour since they changed the export feature some time ago. When you tap an image from the gallery, it opens full-screen but not in editing mode right away. In this view, click the share icon on the action bar (the three circles connected by two lines) and choose "Share as __" for whichever format you want to export as.
After a brief pause, it'll give you a share menu listing apps you can share with, and the top item on this menu is "Save to device", with an icon of an SD card. Instead of launching another app to share with, this will just save/export a file in your chosen format.