Is there a shortcut in Illustrator (CC 2017) to switch between opened documents?
Pretty much every Adobe app that I've used, ⌘+~ switches between documents.
No idea why some are trying to overcomplicate this, when the shortcut is built-in already.
For windows PC press CTRL + TAB
As others have noted, ⌘+~ will switch to the next open document. I would add that if you have 3 or more open documents, you can also use Shift+⌘+~ to switch back the other direction.
Edit > Keyboard Shortcuts....
→Menu commands (dropdown)
→Other misc → Navigate....
– Joonas Nov 11 '16 at 11:43