I have a document in lightroom that I want to edit in photoshop. Do I export? what is a dng?
From LR's Develop module, using the menu: / photo / edit in / photoshop
If you don't have Photoshop setup as an external editor: menu: / Edit / Preferences / External Editing
This will create a new file, send it to Photoshop, then add the saved photoshop file to the catalog when photoshop is finished.